Check out the Gad Custom Cartridges website at
http://gadcustomcartridges.com/
If offers a bunch of cast bullets for obsolete calibers, including a good selection of pure lead balls for black powder arms or cartridges.
Lead balls of .360-inch are sold for $5 per 100. Balls of .308, .311 and .319 inch are also available for the same $5 per 100. That's a darned good price!
Loaded ammo for many civilian and military calibers is also offered by this Medford, Wisconsin outfit.