Audioquest makes a banana adapter for spades that I've used and was happy with just make sure the nut is on tight. BTW I think there is copper or silver.
Extending an existing speaker wire
I have Klipschorns in my corners but would like to rotate another set of speakers on each side of my fireplace sometimes. The existing speaker wires are not long enough. They are terminated with spades right now but I could easily change that. I was thinking of switching to bananas and started looking for a banana "coupling" with no luck. Any other ideas out there?