Do any of them that are sold work for our cars? And if so, where can I find one, and how much power gain would be expected? I'm guessing it'd be between 2 1/2 to 5 horsepower, depending on how hard that pump is to turn....

 

well no one makes one, but to adapt one will not be hard, giving you are willing to take your time on it.
However to keep the belts going the right direction is another story.

You can always just put on a long shaft, and make a braket for the electric motor.

 

I assumed I could just find a shorter serpentine-style belt without the twist in the middle..do they not make them? ..If I routed it from compressor, to power steering, to crankshaft, to alt, to tensioner, and back, the belt wouldn't need to have the twist...it'd all run the same way except naturally the belt tensioner rides the back...

 

I looked into this a lonnnng time ago. Meziere (pronounced mez-Ear) makes a remote mount electric water pump. You mount the motor/pump somewhere in your engine compartment. Then, you drill & tap hose fittings into the existing water pump's housing. Attach hoses to the fittings, and then run the hoses to the electric pump. Problem: None, if you have an extra $300 lying around! Meziere makes high quality pumps, but you'll pay for that quality. 'Fact they're one of the few pump manufacturers with long street-run times. Most electric pumps will tell you "drag race only" because the electric motors burn up quickly.

If you want a look, check out http://www.meziere.com . Wow, they really updated their website! It used to be all text, very few pictures.