Electric hub motors with shimano compatible hub

[Tiddy1]

I have a recumbent trike and I quite fancy adding a 500w hub motor to the back, now as it takes standard 26" mtb wheel that should be fairly easy, however all the wheels I have seen have screw on 7 speed blocks. But what I really want is to be able to put the current 10 speed shimano cassette on so I can still use the 10 spd chain and shifters. Does any one know of a hub motor with free hub?. Some of the expensive electric mobs seem to have them but I have not found one for sale seperatly

[Barchettaman]

TCDM.