Bump! Also, I totally missed the previous posts here. The Stillen Street Radical kits used rotor rings that are near impossible to find now.
Paragon has a couple:
https://paragonbrakes.com/370mm-roto...6mm-thickness/
They are lower vane count than most newer AP Rings (48 vs 72).
Can also change to 372x34 with new hats and a 1mm spacer on the brackets. I think losing 2mm of air gap would be worth it. Might even be able to use the hats I already made for this kit.