You can get a " paste / grease " that contains tiny particles of copper .
I think this is one example ;
http://ecat.burndy.com/Comergent/en/...%23%08false%08
It looks very much the color of copper . When applied to copper bolt connections , it is said to lower the resistance of the surface contact juncture .
You can also get copper bolts , nuts & washers . Those might also lower resistance . Of course , they will not have the tensile strength as steel .
God bless
Wyr