Tractor Supply Company in Canada and the United States are under different ownerships and TSC in Canada doesn’t carry the item Vic found.
For Canadians, I found what I suspect is the same item under the Power Fist house brand name at PRINCESS AUTO, a large chain operation.
It’s a Submersible Trailer LED kit. Fittings, cable, everything for $54.99.
The lens is within a 1/16” of the Monarch #9075 original!
On first examination it appears that the fiberglass bezel on the ARGOSY can be slightly modified to receive the whole unit even more easily than modifying the Monarch housing to take the LED components.
I’ll confirm if that’s the case later.
Sergei