What are the best materials to use for your rest and plate?

I wouldn't say it's the best, but I used to use calf hair exclusively.  I use seal skin now and that lasts a bit longer.  A buddy of mine uses Cordovan leather and that stuff lasts a long time.  The soft side of velcro seems to be popular too and it's cheap for a lot of it.

I was told by 3rivers seal skin wasn't avalable anymore. Where can I get it?

You can no longer get seal skin.

Bear hair and the leather plate.  They last for years and you get enough hair to use two or three times.