The only place I've seen to buy just the conversion cylinder is directly from NAA. If you buy the gun that comes with both, then they are both custom fitted to the revolver from the factory, if you buy the revolver with just one cylinder then later want the other one tou have to send the gun in to NAA to get it fitted. So you purchase the 22lr. Cylinder by contacting them
https://northamericanarms.com/shop/accessories/cylinders/ranger-cylinder/
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NORTH AMERICAN ARMS
2150 South 950 East
Provo, UT 84606
Toll Free 1-800-821-5783
International 1-801-374-9990
Fax: 1-801-374-9998
info@northamericanarms.com

HERE ( https://northamericanarms.com/shop/accessories/cylinders/ranger-cylinder/ ). Cylinders need to be timed and fitted to your firearm. Please contact the factory for further details on purchasing and sending in your firearm to have this feature added. CALL 1-800-821-5783 OR EMAIL: info@northamericanarms.com . I hope this helps!