I've used Surefire Manufacturing. They're based out of the San Fernando Valley and are at all the gun shows. They usually have 400 round bulk boxes of .223 for around $115, before tax. Good stuff, I've used their 9mm, .45acp, and .223 for range use and haven't been disappointed.
NRA, CGF, GSSF, SAF member
Certified Glock Armorer 2011
"Praise be to the LORD my Rock, who trains my hands for war, my fingers for battle. -Psalm 144:1