Do you know where I can find a factory replacement amplifier for the vehicle?

Try this link: http://www.nextag.com/bose-amplifier/compare-html

There are a number of places on the internet that sell replacements but GM purposely makes finding the correct model number real hard because they want all the repair business for themselves. To help them bleed money from unsuspecting owners they no longer sell us radio service manuals or parts.

You can try Googling the model number to find a supplier, or you can go through the dealer and have them send yours to one of their two remaining grossly over-priced repair centers.