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There is a "Kit" available that includes a rifle bolt handle, a bolt to attach it to the rifle bolt, and a drill and tap so that it can be bolted onto the rifle bolt. (If that makes sense.)
Basically, you cut the present bolt handle off the rifle bolt, drill and tap a hole for the new bolt handle and use a threaded regular bolt that is supplied with the kit to attach the handle to the rifle bolt.
Sorry that I can not give you the name of a supplier, but I am sure someone here can help.