is there a performance alternator I can get? Any rcommendations?
or even better a bolt on version from a chevy truck or something that will work?

I ask because I suspect my alternator can't handle powering my amp (power line for amp reads 13v with engine off but drops to 9 when running)

(92 Camaro RS - stock)

 

It would help if we know what alternator you have now? What amp is it?

 

I am assuming it's stock, and I have no idea what rating that is.

 

Look for my thread in the electronics forum. I forget what I titled it, but similar to your thread "higher output alt". Searched under thread originator "sonix".
I ended up getting a CS144 from a 1995 Lumina van. 140A output, and factory reliability. Bolts up easily, just needed to tweak a wire. For a serp belt application it's a bit more tricky, but my thread has info on that.

oh hold on though, your explanation of why you need it doesn't make any sense. I don't think you NEED a bigger alternator, you need to troubleshoot your existing electrical system.