Michael Terry wrote extensively about his explorations. His later travel journalism is less well-known, but probably was much more widely read, in popular mass-market publications like Walkabout and People. It is this material which includes his secret visitor speculations. I have found the following references thus far, but doubtless there are more. This list will be updated when necessary, and any additional references are most welcome.
Terry’s life is documented in his manuscript autobiography, which was completed by his sister Charlotte after his death [Barnard 1987]. A later historian of Northern Territory exploration discusses some of the problems in filling the gaps in Terry’s life, when he had carefully edited the surviving documentary record [Dewar 2009].
Terry’s personal papers largely relate to correspondence from the 1960s-70s and of letters received. He does annotate the date of his reply on many of them, but almost none of his own responses are preserved [NLA 611-1]. In individual posts relating to particular claims I have tried to verify the presumed sequence of correspondence, including letters that are lost.
Michael Terry publications on secret visitors
Michael Terry 1963, ‘Mystery carvings in the Centre’, People, 16 January 1963, vol. 13 no. 23, pp. 27-30.
Michael Terry 1965, ‘Did Ptolemy know of Australia?’, Walkabout, 31, 8 August 1965, pp. 30-31.
Michael Terry 1966, ‘How did Ptolemy get to Queensland?’, People, 23 March 1966, pp. 12-13, 15.
Michael Terry 1967, ‘Australia’s unwritten history’, Walkabout, August 1967, pp. 19-23.
Michael Terry 1967, ‘Were the Spaniards here first? Riddle of Sydney’s rock-carvings’, Sun Herald [Sydney], 10 December 1967.
Michael Terry 1967, ‘When did inland history begin?’, The Inland Review, 2  Dec 1967, pp. 9-12.
Michael Terry 1968, ‘ Were these the first Australians?’ Today’s People, 5 June 1968, Vol. 19 no. 3, pp. 2-8.
Michael Terry 1969, ‘Faces from Australia’s past [Archaeology no 2305]’, Illustrated London News, 18 January 1969, pp. 24-26.
Michael Terry 1969, ‘Spaniards were here first’, People, 18 June 1969, vol .20 no. 3, p. 27.
Michael Terry 1974, War of the Warramullas, Rigby, Adelaide.
This is the only one of Terry’s books written after World War II, and into the period when he became interested in secret visitors. It includes his speculations on links between the central Australian rock engravings and the Middle and Near East. He also discusses the evidence he had previously published such as the Ptolemy coin, the Grey wandjina figure and left it as an unsolved mystery.
Michael Terry work I have not seen yet
Michael Terry 1969, ‘Who really discovered Australia’, QANTAS Junior V-Jet Magazine, vol. 2, no. 1 January 1969.
QANTAS does not seen to hold a copy in its archives [many thanks to QANTAS’s Des Sullivan for trying to hunt one down]. National Library of Australia does not have this issue. If you’ve got one in a suitcase in the garage please let me know.
Commentary on Terry’s theories
Terry’s theories are also mentioned in the following publications by others.
Vincent Megaw  considered the discovery of the Ptolemy IV coin in the context of documented contact between Aboriginal people and early European settlers.
O’Grady’s The ibis seal  is a romantic action story using the premise of an ancient Egyptian colony being founded on the far north coast of Queensland. She weaves in a lot of Terry’s material and references his writing.
Walsh [1988: p. 68-69] discusses Terry’s Cleland Hills find in the context of other rock art around Australia. Thomas Reservoir Rockhole was first documented by Maurice and Murray in 1902, who noted some engravings. Although he visited the site first in 1932, it was his 1961 visit where Terry found engravings. First publication by Terry associated the engravings with Egypt and Assyria because of the face motifs. In 1967 Robert Edwards led an archaeological expedition to document the site [Edwards 1968]. Terry  tried to move the attention back from their antiquity to their supposed exotic origin.
John Mulvaney was less impressed with Terry’s claims. It was certainly him that he wrote about:
Perhaps it should be termed the ‘Lasseter syndrome’. Like Lasseter’s reef of gold, some of these finds have been publicised by extrovert outback characters, unversed in archaeology, anthropology, history or verbal restraint. [Mulvaney 1989: pp. 16-17]
Walsh says although interpreted and recognised as faces, other central Australian perspectives can be read into the images, for example as sitting figures. ‘These “face” compositions appear to represent part of a particular early engraved art tradition’ [Walsh 1988: p. 68]. While they were considered extremely distinctive at the time they are comparable to a now much better known suite of pecked art sites located within the margins of the Australian desert landscape, for example at Burrup, Western Australia and into western Queensland. Different frequencies of motifs may reflect cultural differences, the particular spiritual or secular connections of the site or be a matter of chance.
Rex Gilroy was a regular correspondent with Terry and to some extent took over his mantle upon Terry’s death. They swapped information on claimed sites, and many of Gilroy’s claims can be ultimately sourced to Terry or his correspondents [eg Gilroy 1978, 1995, 2000], although Gilroy’s lack of attribution makes it very hard to sort out exactly what were his sources. Gilroy appears to have accepted all of Terry’s claims without qualification, probably being unaware of unfavourable opinions that Terry had received from academic and museum specialists about the authenticity of some of them.
References [Terry refs are given in full above]
Barnard, Charlotte [editor] 1987
The last explorer: the autobiography of Michael Terry, FRGS, FRGSA, ANU Press / Northern Territory Research Unit, Canberra.
Dewar, Mickey 2009
‘Michael Terry: the last explorer?’ Journal of Northern Territory History, 20, pp. 51-74.
Edwards, Robert 1968
‘Prehistoric rock engravings at Thomas Reservoir, Cleland Hills, western Central Australia’, Records of the South Australian Museum, 15, pp. 647-670.
Gilroy, Rex 1978
‘Egyptians in Australia’, Paranormal and psychic Australian, vol. 3 , pp. 6-9, 29-31.
Gilroy, Rex 1995
Mysterious Australia, Nexus Publishing, Mapleton.
Gilroy, Rex 2000
Pyramids of the Pacific: the unwritten history of Australia, URU Publications, Katoomba.
Megaw, Vincent 1967
‘Archaeology, art, and Aborigines: a survey of historical sources and later Australian prehistory’, Journal of the Royal Australian Historical Society, 53, pp. 272-294.
Mulvaney, John D. 1989
Encounters in place: outsiders and Aboriginal Australians 1606-1985, University of Queensland Press, St Lucia.
O’Grady, Anne 1975
The Ibis seal, Peter Davies, London.
Walsh, Graeme 1988
Australia’s greatest rock art, E.J. Brill and Thomas Brown, Bathurst.