At a Computer Fair in NJ. I bought a couple of extensions about 20 years ago from, what was then, a little company in Brooklyn . . .

http://www.ebay.com/itm/23inch-Internal-IDC-50-Pin-SCSI-Male-Female-Extension-Ribbon-Cable-CablesOnline-/280754237369

. . . you can shorten it to whatever length you want.