I think that is like asking who makes Mopar Performance parts. The only person who knows is the procurement guy and even he might not know from time to time since the suppliers change.

I've never had an issue with JE rings but I'm pretty sure they source from several different suppliers. If you look closely at the JE ring catalog you might pick up some clues since the sizes and shapes might be the same as other vendors.

The other wild card is that JE is part of Race Winning Brands now. They are owned by the same holding company that owns Diamond Pistons, Trend, Wiseco, DART, K1, etc. so they probably have some consolidated procurement power when it comes to buying rings.