The Corbin ones are Aluminum, I think.
There was some talk of using airsoft pellets and forming them to shape in the dies, a while back on castboolits, but mainly for pistol bullets, IIRC.
There was a fella on Saubier that was discussing supplying plastic tips, but something triggered the guy, and he took his ball and went home, so to speak.
I think you are gonna be hard pressed to find a supply of the nylon or plastic tips, without looking pretty hard at DIY injection molding and making your own molds.