stikpusher
How many shades of Olive Drab do they make
I'm guessing that this cuts to the essence of the (unasked) question.
To help a bit, there is a problem, OD is not a very precise thing.
In WWII, there were two distinct ODs, one was for aircraft, the other for armored vehicles. The paint makers sometimes do not specify which is which. To the rescue are a number of sites which can help sort this out, use FS (Federal Standard) numeric color referneces to identify one from another.
Mind, armor modelers often are happiest when they brew up colors to their own taste, which allows for shading and counter shading, and sun fading and the like.
Another route is to get a MiG or Vallejo color set suitable to the subject--like "Early US WWII Armor." Some of those are already thinned for airbrush use, too.
Your model, your choice.