Well, as much as I'd love to see it happen, I don't see a way. The only way you will be able to make a 100% accurate to the game ammo counter is with complex processors and computers. And to be honest, I don't really know if you will be able to do that.
The most accurate and easy way you will be able to do it would be one of thatdecade's counters. If you haven't already noticed, you are able to choose the ammo count, colour and the fire type.
And of course, the free version will be the graphic I mentioned.