The main manufacturers are CCI, Federal and Remington
"Without a primer, a cartridge is so much scrap metal. Richard Speer founded CCI to provide a steady source of component primers to reloaders. Primers were CCI's first product, long before Mini-Mag™, Stinger® and our other well-known ammunition products.
Our primers are highly evolved products because we continuously test and improve. Today's CCI primer is more sensitive, easier to seat, and more compatible with progressive and automated loading equipment than even before. CCI primers have always incorporated modern non-corrosive and non-mercuric initiator mixes."
"If you're a reloader, you want components that will do the trick every time. Federal® offers a full line of primers and wads to meet your needs. Gold Medal® primers are manufactured to exact tolerances for the best of your loads. Federal Premium's heralded brass will now be available for rifle and handgun shooters. Now it's easier to load your own."