I ended up buying some Briggs and Stratton brand RJ19LM plugs packaged in the USA which are in a cardboard blister pack with the big B&S logo on them. The plugs inside are in fact Champion plugs. I reckon that if Briggs and Stratton recommend them, well at least they must be willing to call the product their own, regardless of where it was made.
I am not promoting any single brand here. Just trying to sort out the best alternatives from what has become a very limited set of options.
