Re: WTB:300 Win Mag Brass Lapua,RWS
You've picked the best two brands, in my opinion. Best meaning that RWS and Lapua are dimensionally very uniform, and they have about the toughest case heads going. If you're happy shooting moderate pressure loads, Norma brass is generally of consitent dimensional quality, but Norma brass has a consistent reputation of having softer than average case heads, meaning that the primer pockets will swell at pressures where the Lapua and RWS brass operate at very comfortably.
Other than those three, I'd go Winchester & Federal, and then Remington.
The two brands I'm aware of that are consistently head and shoulders above the rest are RWS and Lapua. And they do cost more than the plain-Jane brands.