I've just added an FAQ entry to the pmax webpage for this
	(thanks to some info from Brian Chase (bdc@std.world.com):

It is DEC part # BC09J-03 which is a 68pin female to 50pin centronics male
SCSI cable. Ficomp may stock some of these cables. 
www.ficompinc.com

> I'm trying to get NetBSD installed on one of my 3100s, and I haven't
> yet been successful with the net boot, although I've got this to work
> with both DS/25 and DS/240.  I do have some spare external SCSI disks
> with working NetBSD systems however.  But I can't seem to find a cable
> to hook to the port on the back of the 3100.  The port is male, with 
> 68 pins.  I contacted several mail order places, such as ComputerGate,
> and Dalco, to see if they had a SCSI cable available for this type of 
> connector, but no luck.  What's the normal procedure to hook up a 
> disk to one of these fellows?
> 
> Doug
> 
>