I had an ebay search going for quite a while. Only once did I get a hit and that was for a complete cooker in Dartmouth, NS.
I too would like to find a US source.
Taylor has spares kits. I presume you can order from them in England
Other than that you could try St Brendans Isle, the mail forwarding people. They are the US distributor for Lavac
toilets, of Blakes, Taylor, Lavac, so maybe they can source them.
Let me know, I would buy one or two myself.
Also, my boats PO bought a couple of Portugese units. I tried to put one in this summer and the fitting was different. The treads were the same but the bottom of the male fitting extended down with about a 1/4 of unthreaded body that held the burner unit too high.