I got a 338 Edge from Shawn Carlock last year and bought a set of his 338 dies at the same time. They are basically a set of Redding dies that Shawn machined to fit the 338 Edge. They have a tapered neck expander that takes your 300 RUM neck up to 338.
As far as brass, I am aware of only 2 brands for the 300 RUM -- Remington and Nosler. In my experience, the Nosler is not worth the extra money as the primer pockets loosen after 1 shot. The Remington brass does fine. I shoot Shawn's suggested load for the 300 SMK, and the rifle & load shoot under .5 MOA. Took a Colorado bull elk last year at 648 yards with my RBG (Really Big Gun).