Like browner said, you don't need 17's. It's not the rim diameter thats important with these brakes, it's the rim's width/offset and spoke design. I am running the same brake set up with GC 2.5RS rims (the same as the JDM GC8 ver3-6 (???) rims).
The point is the are 53 offset but 7" wide instead of 6.5 inch wide like WRX and new 2.5RS rims. You need to get old school Impreza 16's or some wider, lower offset rims.
BTW the Subaru 4 pot calipers are sick! Work so well and let you keep 16's :bigup:
You should be able to get these brakes on any GC STi clip.