If you put a WTB thread in the F/S section I'm sure you'll find someone willing to sell you their amp.
Depending on your mileage you may be able to get a new one from Mazda under warranty too.
As for replacements, I don't know any off the top of my head that fit right in. Just take some measurements and do some searching on sites like www.crutchfield.com and www.sounddomain.com.
I have a stock amp working that I'll sell you for $100 shipped OBO to the lower 48. It's still installed but I'm planning on pulling it out. If you want it I'll pull it out the say you put some money in the paypal. PM me if you really want it.
