Good luck, Donnie. I think they're pretty rare. Marlin listed the Model 90 Skeetking before WWII, but I don't know whether they continued offering that model after the war, or for how long if they did. Likely someone here with Marlin catalogs might be able to tell you.

I'd bet a Skeetking in most any gauge other than 12--especially .410--would be REALLY rare!