Starline would be my first choice, but their website doesn't show any in stock right now. Grafs.com has Starline 9mm nickel in stock right now, though. They don't have any nickel .308.
For NEW cases, that probably ranks up there with primers. Good luck... Now previously fired, I bought 500 nickel 308 from redeye reloading a few months ago. No idea if there's any still available.