I have some 6BG6s which are very similar, but a bit less powerful so they're physically smaller. You are welcome to 4 for £10 if you want them. They're basically a 6L6 with a top cap. They're branded Zaerex but appear to be Russian.
http://www.mif.pg.gda.pl/homepages/f...37/6/6BG6G.pdf
Paul