There are MANY samples of stock out there that fall under these terms. The problem is the type of weave in the web and the color khaki itself. Many of us have seen dozens of pictures, ALL looking slightly different. So what is screen accurate?
I thought it a good chance that Indy might be wearing an authentic belt from WWII. So I figured a good place to start would be those fellows who re-enact war. They MUST be as picky as we our about our subject. Here's what I found out about WWII Khaki. It's really NOT khaki, it's Olive Drab No. 3 AND this shade can very amongst the manufacturers of the time.
Here's some pretty interesting reading.
http://www.atthefront.com/khaki.htm
What color is the "right" color? There are many of them...
Despite rigid government specifications, "od" or "khaki" is not one single consistent color. All WWII uniforms and equipment exhibit a wide range of color and shade variations. When millions of items are produced, perfectly matching shades, even of the same color, are rare. With regard to od 3 (olive drab no. 3), originals range from olive, to pea green, mustard-brown to olive brown. There is no single correct shade. However, the later, a light olive-brown, is generally regarded as the most desirable. That's the shade that we go to great lengths to duplicate.
Further complicating matters are the peculiarities of light effects- in fluorescent or indoor light, even the happiest of khakis often appears more clearly olive. The same item in sunlight will usually appear much more tan or brown
OK, now that makes things soooo much easier.

But my guess is, since all these re-enactors like that particular shade it probably was the most commonly found. So today's re-enactor reproduction manufacturers are more then likely trying to reproduce such a color in their belts.
So here's a list of re-enactor reproduction companies;
Where to Buy
http://3rdidreenactors.synthasite.com/where-to-buy.php
Quite a number of places carrying these belts made by Mil-Tec® out of Germany.
Their product carries the name SEMS Inc. on it.
Quotes about their belts;
"Here you go! Own this faithful look-alike of the real ones issued over 60 years ago to our brave troops during the Big Red One."
"Our reproduction of the standard GI khaki trouser belt is right on. It's the correct OD color with black tip and comes complete with the black, open faced buckle issued to all Enlisted men. It's manufacturer marked SEMS INC. 1942."
Pictures of authentic and Mil-Tec® belts.
http://www.flickr.com/photos/35223822@N ... 430706242/