You can get one used on the boards(good idea) or go one of the supporting vendors like Jack or Bweavy, both very good guys. I have a PT54 that can be rebuilt if your interested.
Would that be a Garret .63 or PTE .63 exhaust housing?
Try a vendor such as Cotton's Performance, Lubrant Performane, or PT&E, or Full Throttle..all are great vendors to deal with.