The early Savage 99 250-3000 had a barrel twist of 1:14 that won't shoot anything over 87gr accurately. In 1960/61 Savage changed to a 1:10 twist rate and you can find bullets (bullets only, not loaded cartridge) up to 120 grain that will fire accurately.

You will most likely need to find someone that reloads to get ammo. I have seen new brass available.