Penny - there's some info, and a few photos - not many - of the place just post the RRAF taking over in 1955
here.
There are quite a few photos at a website run by a chap called Tony Hawes who was at Thornhill from 1951-63 - see
here
There are quite few photos which aren't of Thornhill, but you'll find a few, including an aerial view or two. (I have a suspicion that this chap might be the ppruner 'warmtoast', who's put some photos of Thornhill up before).
There are some photos in a Flight article about the 1953 centenary event, which are on pdfs
here and
here (the fatal mid-air being dealt with in a very brief, matter-of-fact line on the first page).
You might (I can't recall) find some info and photos in Beryl Salt's
Pride of Eagles book.
You'll also find some info
here and
http://rhodesiaandtheraf.********.com might help - you'll need to replace the asterisks by taking the words 'blog' and 'spot', and putting them together to form a single word and cutting and pasting into your address bar for that one though, as the word formed by this amalgamation gets filtered by Pprune.