Thanks for all your replies. Once I reralized I needed to specify "Shimano Positron" (not Nexus!) I found at least two sources on eBay with old stock and ordered the assembly. So in a few days I should have it back in working order.
It is a coaster brake LH hub as Aaron mentioned. This didn't keep my from adding a set of inexpensive handbrakes form Niagara Bike Works (and fenders) since I was accustomed to hand brakes for years. So I've created some kind of hybrid beach cruiser-commuter-English wannabee vehicle. (Changed the handlebars to "moustache type from the wide cruiser style.) Next step, as RHM suggested, is to just go out and get an old Raleigh and play with that!