My recent experience with this problem is that it's best to send it to Ruger and the cost would be $130.00 and yes, it would have to be fitted. In part, that would indicate that buying one at a Gun Show, is hit and miss. ...
Sad but on more than one occasion, I have seen orphaned cylinders at gun shows. All had serial number engraved and always thought it would be nice to get them back home ...
Be Safe !!!