Bryan Quick6 might have one.
Power Seat Track & Switch
You should have the newer 3 motor set up in your 87. Any 86-87 G-Body split bench with a 3 motor track will work. The tracks are G-Body only. Now if you need the motor assemblies, those are used on a lot of GM cars. What you'll need to do is drag it down and match them up. Full size B-Body GM cars from 87-96 use the same motor assembly. The part I call assembly would be the steel mounting plate with the 3 motors riveted to it.