Yamaha DTXpress/DTXplorer/DTXtreme

Hello Folks,
Well after blatting and biffing my new DTXpress3 for a few months 
now I want to try downloading/loading some extra kits. I have tried 
in vain to get hold of the "special" data lead but after touring the 
usual retail outlets I have so far been met by blank looks and 
shrugging of shoulders.
Do I really have to go direct to Yamaha and pay god knows what.
Do any of you guys out there know where I can get the lead in 
question, Oh and by the way does the P.C. end have to be a serial 
port plug, I would prefer a USB.
Cheers for now.

Alan (Rav4t3)