UPDATE!
The fork came in but I'm out of town right now so I'll be picking it up when I get back. The guy on the phone couldn't find a model name but read out what he saw on the packaging: "TK" "coil" "100mm" "26". Based on that I think it is the Rockshox 30 silver TK model. It has mounts for caliper and disc brakes.
Also the shop I took it too is REI so I don't feel as bad about not giving them the business as I would a mom and pop shop. I'm doing this on behalf of a nonprofit I volunteer for so one of the other volunteers who's done this type of thing before will be replacing it. If it was for me I'd have REI replace it so I don't have to deal with the hassle, they'd only charge $45 for it. If I can leave the shop employee who sorted this whole thing a tip I will do that. Or put in a good word with their manager or something (but I think he might be the manager).