Yes you can get brass & dies
Follow the links
https://www.northernshooterssupplies.com.au/300-Rook-Unprimed-Brass-Cases-p/300rk.htm

I have to agree with you there Hendo - what would be your load?
Also it is a .300" projectile - casting will be in order, or will you resize .32-20 pills?