While I no longer have any information on the vendor, 8-9 years ago I was able to obtain a slot mount from one of West Marine's vendors of Bell's and other Brass works. The name was given to me by one of West's customer service
people and I was able to track them down. Several weeks after sending a letter of inquiry, the mount arrived free of charge by return mail. A little grinding and the thing worked perfectly, and allows us to move the bell from it's position on the bulkhead in the Salon
to the second mount on the binnacle in the cockpit
for use in fog
(tho' frankly, we've never needed it). You might give West a call or simply visit one of their stores to see if the maker's name is on the packaging.