The Tamiya Ford quad, limber & 25-pdr have just been re-released so should be coming back into model shops soon, Hannants in the uK are saying that they have it in stock and they do mail order. £14.99 UK or £12.79 plus shipping export.
http://www.hannants.co.uk/
The Italeri quad is a bit more tricky - just a case of trawling the 'net I'm afraid - there are still a few around - I don't like it myself but Ebay seems to get quite a few models on it- I know afew people that get a lot of rare stuff from there.
I have a spare body and some other parts left over from conversions but not a complete kit, if they would be any use.( modify the radiator and stick the chevy body on the Ford chassis? - I know it wouldn't be 100% but the body is quite distinctive as a difference between the two)