front or back? there is a back one in the V classfieds...and if you dont want that, there is a sticky in the V forum that says V parts wanted, that if you post in there, they might be able to hook you up
Then you can go to any GM dealer and order what you want. GMPartsDirect.com will get anything you want shipped to your house. Be aware there is more to just the bumper cover when doing the conversion. Total parts cost (grills, fog lights/brackets, inner fenderwells, etc) are going to run you around $800-$1000. Paint would be on top of that.