I pulled out the illustrated parts manual, and found the GM part numbers. Unfortunately it lists the entire mirror as one unit, and does not separate the mirror glass, motor, etc.... out. If you want a copy of the page from the illustrated parts manual, just let me know.
Driver's side (without heated mirrors) 14047599
Driver's side (with heated mirrors) 14049035
Try cross referencing those with a GM dealer or website, or see if anyone has an '85 or later parts manual....