der_nanno said:Dimecity-cycles sell them as well and no, I haven't got one for you, so most likely it will boil down to importing it.
You may want to contact these guys in Germany and ask them, whether they would be willing to make a megaphone for you from scratch (but it will certainly be more expensive than the one from Cone-Engineering, maybe even with shipping and taxes figured in):
http://www.auspuffschmiede.de
Cheers,
Greg