The 7mm LRM brass is very had to find, pretty much other than straight from Gunwerks and the very rare random online listing, it's nearly impossible to find. And if GW has some, I'd buy about 500-1000 cases, if that is a caliber you plan on committing to for many years and many barrels. Never owned one, so can't comment on performance, but it appears to be about dead-center between the 7mmRM and the 7mm STW.
7mm RemMag, brass and ammo can be found everywhere. It's a great caliber, been around since 62, and ain't going nowhere anytime soon.
7mm STW another awesome caliber. Brass and ammo can be found in a lot more places than it used to be, but the availability still falls somewhere in between the 7mmRM and LRM. It's also a commitment-caliber, because brass seems to appear, then dry-up. And this happens in random spurts. So, if you plan on committing to it, I'd stock up about 250-500 cases and that should last you several barrels. You will also be hooked after owning one.