It looks like a RG 66 Super Single Action, which came with a .22LR and a .22 Mag cylinder.
It probably dates back to the 1970's and, like most RG's, has little value (<$50). They were not known for their quality.
The best place to find RG's is a municipal gun buy backs. Looking for a .22 Mag cylinder may be a futile waste of time.
Have you fired it? If so, is it at all accurate?
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