You can run the rears from the 2001- 2007 wrx (2 piston fixed calipers) if you get an adapter from KNS brakes. They'll use the rear rotors from a BRZ or 2010+ liberty gt I'm fairly sure.

Other options are sti brembos, ap racing, wilwood and stoptech (may need wheel clearance).

If you're on a tight budget, 2004-2008 liberty gt rotors and calipers can be had at a decent price, and have just slightly smaller rotors than the sti brembos.

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