I realize this is an old thread, but for those who come here looking for answers:
Best i can tell RCBS still makes a 308 small base die, but discontinued the 300 WSM small base die.
Forster, Whidden and Warner will make you a custom die if you send them two cases. Not cheap but a solid solution.
PVA is not listing their push through die for sale anymore, but who knows, if you call Josh and ask nicely, and they are NOT super busy, he might be persuaded….
Porter Precision Products in Lake Jackson Tx made me a custom die at a reasonable price, by modifying the Redding body die. I sent Kenny two FL sized cases with the Redding die. Superb workmanship.
Works great, the fired case is now sized down 2.7 thou at the 200 line near the base of the case.
Btw: Recutting your chamber a tiny but larger at the base might be the best solution.