Wow, even I don't remember that one.
Craig O'Connell's website (last updated in 2014,) where I see a link to AM for it listed.
Your best bet would be to check with American Models directly. The GP35's haven't been fast sellers, they probably still have some in stock.
What I can tell you is the GP35 is a pretty decent, basic model. Handrails are Delrin or some such plastic, there are no grabirons, either molded or separate. The body is in three pieces: main body, cab and dynamic brake (or non d/b, depending on roadname.) Most, if not all have the "spring drive" meaning a spring is used to transmit power to the trucks instead of a set of universals and shafts. It works, it's just funky.
These things were made in 1992, so they're not quite up to contemporary standards. If you're interested in the overall detail level, here's a shot of when my two GP35's were primer-liners, prior to final painting:
There's only some slight modifications made: locations for grab irons are drilled out, lift rings added, air horns drilled out and a small MU receptacle added at each end of the locomotives. Otherwise, they're straight AM shells.
Rusty