Most UK Supra owners use ADL Bluepint as a direct replacement for the stock discs which they order from their local motor factors. The US seems to have more choice for Toyota parts stores, you’ll probably be able to obtain high performance discs for what we would pay for stock discs.
http://www.blueprint-adl.com
http://www.alldiscountautoparts.com/ToyotaSupra.html
http://www.toyotapartstore.com/toyota-supra-parts.html