If the oil control rings are one piece items, then unfortunately you can't get them anymore. They have been made obsolete.
I had a problem with a 900 customer with the very same problem.
The later 3 piece rings run in a thinner groove so you can use them either.
2 solutions. One is to get a hold of the later pistons and rings, or secondly use it as a good excuse to throw in some aftermarket hi-comp jobbies
The latter would be a cheaper option i think.