Yashica AFAIK offered two kinds of hoods - rubber cone shaped (slip-on type) and straight metal slip-on. Both are black so both fit GT. I'm not aware if GT model had special hood.
I'm pretty sure any 57mm slip-on hood for standard focal length lens would work. I have 54mm slip-on metal hood for Petri, which fits Petri 7s and Lynx 5000 and....hm, some other camera with 52mm filter thread 🙂