Hello Rory,
There are several files that have NOT yet been digitised at the National Archives of Australia’s website, for James Frederick Matthews.. One has, it’s barcode is referenced 8215765. There’s 36 pages digitised. From that file, here’s some info.
Enlisted 9 Feb 1916 in AIF. Discharged London 6 Feb 1918, and boarded ship for India with others recently discharged from AIF, bound for Wellington Barracks, India.
9 Sept 1922 in a Letter to your chap from the AIF Major at Base Records, Victoria Barracks, Melbourne Australia your chap’s then address was:
Lieut. J.F. Matthews, 39th Garhwal Rifles, I.A., c/- Army Department, 6 Esplanade East, Calcutta, INDIA.
http://www.naa.gov.au/collection/recordsearch/index.aspx Sorry, but I don't know how to search for Indian Army Records, but the above info may help other RChatters,
Fingers crossed

PS, re the rest of the files at NAA ... you can apply for these to be digitised, some may refer to other AIF chaps with same or similar names.
Cheers, JM