only ever made my own once...
not even anything usefull for you just a bottle of graphite powder mixed with woodglue
it being conductive was more a side effect for me really...
but knowing that.. it was fun to play around (making paper circuits and stuff) but I wouldn't say that'd be an option to make anything usefull really... maybe my mx wasn't good enough IDK.
But I might be wrong... since you only need to leave the "terminal" part of a metal part unpainted... you might paint that terminal with a mix of graphite and woodglue
(the more graphite the better.. you can add water to thin it down if it get's too pasty)
I think it might be good enough to keep the terminal from rusting too quickly.. if it's conductive enough for whatever you need to do though IDK.... that needs to be tested.
oh and it comes in the best of all colors... dull grey...
I'm not sure you'd be able to tint it in...say... bright red [maybe with copper powder... *shrugs*]
Anyways.. graphite powder
(mine was a dry lube in a bottle .. not a spray can... but it's available at art supplies as well... amazon.com has it)...
and woodglue.. common things to have around, not?
so maybe you can just give it a try without actually having to buy anything
'sid