Carpathian, here are some copper units. I tested and liked the Furutech FPX-Cu and the Oyaide R-0, but the Oyaide R-0 is better in my mind. The ACME is very good, but silver plated
Furutech does have the FPX-Cu receptacle which is phosphorous copper, because pure copper is too soft to provide strong contact - $63 Cable Company
Acme Audio Labs have silver high purity plated copper - $65 Acme Audio Labs
Oyaide R-0 highly polished beryllium copper (same here, not pure copper because of clamping strength) - $151 Cable Company
Shunyata SR-Z1 high copper content brass - $100 Cable Company
Not sure that is all, but those are the ones I know of