They are not worth a whole lot. I bought one online for 150.00 and since have been told by gunstore owners that they sell for less than that. There is one on gunbroker.com now for 150.00.
Beginning in 1956, Sears Roebuck and Company produced the world's first gas-powered gun under its J.C. Higgins brand. The gas system was produced by High Standard Manufacturing.
One place to check for a magazine for an older model .22 rifle is at a pawn shop that trades guns. Another would be neighborhood yard sales.
Sears Roebuck Model 3T 22 semi-automatic were made during the 1950s and 1960s. The guns were made by Marlin in the 1950s, and are worth between $300 to $400..