The two that come to mind are the mentioned Buffalo Bore and Double Tap Ammunition. They both specialize with bullets and velocities that are much better than off the shelf standard pressure 45 Colt ammo. You have probably figured out that store ammo is mostly loaded to standard pressure and more suited to Cowboy action shooting, rather than hunting. And the premium standard pressure stuff is likley to come with a fast opening hollow point that is better suited to self defense rather than big piggies....
Craig