Scope ring screws.
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Any half decent gun shop should have some. Either from old rings or from a kit that contains different screws and lengths. A lot of the older shooters have a few old Weaver rings in the junk box. Many are tightened too much, and it strips the threads in the aluminum bases.
If you have a Gun Show in your area, lots of vendors have parts boxes, and you should be able to pick up some fairly cheap, or even buy a single ring that has the screws in it at a gun show.
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