I looked into doing this a couple of months ago. the only thing I could find was made by Niles Audio but it only had spring clips. I gave up. If you find one, let me know.
Yes there is one out there that I am currently using but I don't think it will take spades. Its made by Niles (Cost Around $80) and it consists of only a push button. Out for amp #1, In for amp #2 so one of the amps is always one line with the speakers. I have this set up for my home theater so I can switch between my HT Received and a McIntosh 2 channel system. Works great! Good Luck.
What happens when two amps are on at the same time, one wins and one loses. The loser ends up in the repair shop.
I did this when I was young, not the best equipment. JVC receiver and a Denon poa-2400 or something along those lines.
Granted with better designed amps that shut down with a short this might not happen, but I will not try this again. All it takes is one opps...
Use banana speaker terminations? Easy to switch.