Heads are available, at least the guys in Germany can buy them:

http://www.thomann.de/de/marshall_mr1992lem.htm?sid=af5f37f9493b33c440c3c727666766ca

I really would like to have one, but I can't justify spending the money....I'm happy with my Gallien-Krueger head.
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MHB 3039
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After listening for over 30 years, searching and waiting for alternatives, I understood that there will be no other band like Motörhead. Never.