Have you tried Numrich? They got a lot of the older Colt parts. Also, have you tried Colt?
Have you actually tried either of the new ones, that is installed it and fired the gun? The reason I ask is that very often a maker will upgrade and change the appearance of a part for one reason or another, and then someone with the old part thinks that the new one is "wrong", even though it will fit and function properly. I recently got a part for a washing machine; it came with a big red notice saying that even though it did not look like the old part, it would work. It didn't, and it did.