Will This Help?
Finding an OEM amplifier is nearly impossible for subwoofers and in many cases not the best route to go. Two slight possibilities. Apexjr.com might an M&K amp on surplus. I saw it on there recently. When you go in, click on amplifiers and it should take you to it along with others.
The second and probably better bet is one of the replacement subwoofer amplifiers from partsexpress.com.