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If one fell out and you have the other one can you measure it?
Harbor Freight has tools to measure bolt thread and pitch - I have one that is a metal disc with holes on the inside to measure bolt width (for example, a standard "10mm" head bolt is 6mm) and has teeth on the outside to put against the threads to measure thread pitch (same example, 1.00mm thread pitch).
McMaster-Carr is an excellent resource for ordering bolts, you can get fancy stainless steel bolts, socket head, whatever you need.