Ahh... that's my baby. I've owned 2 1970 GSX's in real life and one GS, all with 455's.
Anyway, the only place that I've found so far for the factory rims is here -
Scale Equipment Ltd
But I'm just getting back into model building and built 3 out of the
box old Revell's GSX kit's already before I learned about places like
here and aftermarket model parts.
Aftermarket rims & tires -
Pegasus Hobbies
Detail Master /
Satco Tires
Good luck
"Fast with class"