Gee, I'm having the same problem! Lyman's 48th and Nosler's 5th loading manual editions have the .300 WSM, but it's so new a cartridge, that nobody seems to have pet loads for it yet. We're the guinea pigs, I guess. Seems like a darn nice cartridge. Haven't shot anything but factory ammo yet, due to not having dies. Hope to rectify that ASAP.
Anyhow, get yourself the Lyman or the Nosler book and let's hear of your results! Enjoy!