Believe it or not, it's not hard to come up with everything you need to injection mold. There's a company called Smooth-On who makes all the materials you'd need to make silicone molds as well as the synthetics that go in them. Some of the synthetics they make are up there with stuff like Nylon 7. One of them (I forgot the part No.) is very soupy and is very good about getting in to small spaces without leaving a bunch of bubbles. Most of the synthetic molding that Mythbusters does BTW is done using Smooth-On products.
Mold making takes allot of planning though. It can be easily messed up and often costs a pretty penny to do.
I have a hunch that tac rails are going to slowly move away from the weapon field and in to the every day world. I just see more use for them in every day life while the weapon world is slowly moving away from that sort of thing towards more sleek component systems.