Remington was the Company that pushed the 7mm STW. (no other company i can find still chambers it either). I did a search on their website and It seems that they have discontinued chambering any standard setup for this cartridge. It seems that they have chosen to promote their 7mm RUM instead. I believe that Remington will still make it out of the custom shop, but it'll be just as expensive as a total custom made by a gunsmith.
I know a gunsmith who has rechambered many exhisting 7mm Rem Mags to 7mm STWs with great success. You have to Set the bbl back 1 thead and run the reamer to properly cleanup the chamber. The magazines also have to be modified to accept the longer STW.
Brass is usually hard to find with the companies usually running 1 batch per year, but it seems that Midway USA just recieved a shipment as they have all of the 7mm STW brass quantities available.
Interestly enough, they are out of 7RUM cases.
.338 Weatherbys are really expensive to shoot as a the Ultra Mags if shooting Factory stuff, but the .338 Win mag is the cheapest. You can shoot a .338 Win Mag 500yds, but it also has a trajectory similar to the .30-06.
I'd opt for a .338 Ulra Mag and have it custom made. Remington only chambers the .338 Win or .338 RUM in the Model 700 XCR, I'd want a diffrent setup.
Dan