Found these thought it might be helpful for you guys. I might get them myself if I am unhappy with my pedal after new pads and some new ATE super blue
http://cgi.ebay.com/ebaymotors/05-06-07-SUBARU-WRX-IMPREZA-STI-BRAKE-BOOSTER-EJ257-_W0QQcmdZViewItemQQhashZitem3360386a63QQitemZ220657642083QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories#ht_766wt_941
http://cgi.ebay.com/ebaymotors/2004-SUBARU-WRX-IMPREZA-STI-BRAKE-BOOSTER-EJ257-GD7-_W0QQcmdZViewItemQQhashZitem4cf34393a3QQitemZ330498806691QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories#ht_766wt_941