From Cessna "Electronic Installations and Service/Parts Manual":
Item 29 -- Block -- Mounting -- 0431016-1
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www.cessnaparts.com [
cessnaparts.com]
0431016-1 Info -- BLOCK In Stock -- $120.51
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Or, maybe find a used one somewhere, or maybe have one made. I'd probably just buy a new one, outrageous as the price is...