a member on the Acadia forum added all the tow package parts himself. I think he had an 07 or 08.
But here is his parts list.... Note the tow haul button....
This can give you a start on the dealer locating a part...
Ok, I have been searching and collecting a lot of information to add the FACTORY tow package to my Acadia.
I believe this will be very helpful to everyone who doesn't have the tow package.
Below is the list of parts you will need:
20781543 The Hitch
11515776 Bolts for the hitch (need 8 )
12191503 7 pin plug receptical
25910884 7 pin harness
25856252 V92 fuse block (without HID), or 25856249 V92 fuse block (with HID)
15249974 Tow button (with power liftgate)
20772530 HD radiator
25802203 Trailer brake controller