I’m setting up two 12-inch subs with 2500 RMS and a 2000-watt amp, and I’m pretty sure the stock alternator isn’t going to cut it. Even adding a second battery might not help enough. I tried getting one from JS Alternators, but the mounting holes didn’t line up. Heard bad stuff about Power Bastards, so that’s a no-go. Any suggestions?
Try these guys: Autotech. They’re reliable and have a solid reputation. Should be worth a look.
Find someone who can make a custom bracket to hold the bigger alternator. Might need a bit of welding to make it fit right. 
Custom mounting bracket could solve your problem. Maybe also check back with JS Alternators—they might have a fix for this.
Autotech Engineering has a plug-and-play unit that should work for your car.