Has anyone identified where the original grips on the gun came from?

With all the off-the-shelf parts on the gun, my gut tells me that the grips are off-the-shelf too and not fabricated.

Making them is not an issue (nor acquiring a good replicated pair) but has anyone found a good substitute that looks shockingly close?

Don't say Gum-out bottle!

I've heard something about wheel chair handles or something like that. You just need to look around for anything related to “handles” in general, you might get lucky and find something we can all use.

The gun grips were actually hand carved out of wood. For a good substitute, I suggest going down to your local bicycle supply shop. They should have some ones there.

For the grip on the barrel of the gun i heard of using the container from carb cleaners. they have a nice formed grip. otherwise you'll have to carve one out of wood.