The throusers-belt is a WWII Army Officer's style cotton web belt used to hold up his pants. The web belts changed slightly during the three movies. In Raiders and ToD the web belt is dark brown and in LC the webbing belt is a light brown/khaki color.
The gunbelt was basicly the same in all tree movies - however the whipholder was permanently attached to the gunbelt in "Raiders" and in "Temple". In "Last Crusade" the whipholder was slided on. See whipsection.
The gunbelt is 3,8cm wide (1,5 inch), and is actually quite ordinary. As for now best sourche is Noel Howard at M.B.A. but as from September 2003 M.B.A. is closing down, so a new search is to take place...
The brown webbing belt is rather hard to find, but the kaki-one is to be found in any Army surplusstore. And usually quite cheap to.
All You need to do is some distressing with fine sandpaper (grain 120), and maybe 2 - 3 times washing (without the buggle) and
Your belt is ready to go..
My gunbelt is nowhere autentic, however it is licened by Lucasfilm. The original do not have a brass-ending, nor do it have the stitching along the edges, and finally the holder is not a leatherstrap but metal (propperly nickel).
But here is is:
Belts on Indy: And on me: