Tough order on oversize pistons for the 500T. The engine uses the same bore as the CB450 and CL450, but a longer stroke. Thus they use the same cylinders and piston rings.
Wiseco would be able to make a custom set of pistons, but that will run about $350 to $400 for the pair. The other option would be to either swap your cylinder out for one with less wear and go back with the stock pistons and rings.
Another option would be to send your cylinders off to a company like Millenium Technologies and have them nikasil coated which would return them to stock diameter, thus running stock pistons and rings.
You can run CB450 pistons in a 500T but the compression will be much lower since the piston sits lower in the bore as the wrist pin height on the pistons is different.