I found a guy in Texas and of course Hitchcock's in UK, that sell the Bosch plugs. Highly priced, but I got a bunch of them for me and my pals...all running a Royal Enfield Classic 350.
Odd that plugs are so unique for this motor, and until now, haven't been able to verify any alternatives...maybe the above will work, but I've got a few Bosch's now, so no point in buying more...