Being on a rimfire kick lately, I picked up a New Model Ruger Single six.  It is well loved, but tight.  Serial number puts it end of 1977 early 1978 production.  It came only with a .22lr cylinder.  The frame is marked .22 cal.  Were any of these sold as .22lr only, or can I get a .22 mag cylinder for it.  

Other than plinking, I intend to carry this revolver while small game hunting and sometimes .22 mag could come in handy.  

So to understand, based on the markings on the gun, it's not exclusively .22lr if I buy a .22 mag cylinder??

Yeah, when I looked into the actual cost, I figured leave as is.  I already have a dual cylinder Rough Rider if I see the need for .22mag.  I figure for hunting backup, I'll just load it with hyper velocity segmented ammo. I admit that I'm sorta stingy with my .22mag ammo as I only buy Hornady Vmax for my Savage woodchuck rifle.  I would only use the revolver to finish off one that's down but not out and .22lr should work fine for that. I think in the last 18months I've fired 6 rds of .22mag through my Rough Rider, just to try it out.  It worked and that's really all I needed to know.  

In your case, going the other way, I bet that aftermarket company could easily make you a cylinder that would work.  At $135 the cost savings on ammo + your enjoyment may very well be worth it. 5 cents a shot vs 35 cents a shot is a big difference over time.

Yeah if I see one cheap enough, I'll take the risk of it being a drop in fit.