The other source is
Both spares and base camp sell the burners. Both ship internationally for little cost and with quick service
In recent years Hanse from Germany has started making replacement burners of very high quality and performance. They are not cheap
Toplicht would not sell to me in the USA. But only alerted me to this after accepting my order.
I need to add a caveat. The burner you want is NOT the 4 legged variety. You want the 2 legged type. The 4 legged type has a great deal more mass than the 2 legged type and does NOT Preheat or simmer well. If you try to summer, turn the heat down, the burner will cool and not work
right, it will flare.
Both Base Camp and Spare should be aware of this and will respond if you send them an email
I just checked and both sources are saying “out of stock”. If you find out what the story is please post here.