AJ, you really should not have a problem finding it in that country south of Detroit. LOL I know that Home Depot has a sister company in Canada but forget the name now. I can find it if you need it.
On this side, Lowe's, Aco, Damman Hardware or Home Depot, among many others should have it. If you really can't find it, try a hobby shop. Rider's (locations in Utica, Madison Heights) or one of the places in Port Huron would certainly have it. Kind of shows you what a misspent youth I have had, eh?
If you are trying to fix the mirror, I think that 1.) I would check Storm Seal (I-75 at Big Beaver exit) and if they don't have a better idea, I would use clear epoxy for the repair. Granted, I haven't seen it and you could very easily be on the right track, but if you are missing a small chunk, 5 minute epoxy and masking tape might help. I would only do this as a last resort and on something where I realized that it was not a permanent fix.