These guys sell them.
http://www.usbfirewire.com/Parts/rr-apex-xxg.html
They aren't cheap but they are made specifically for the APEX.
You can't get a repeater in the line or it will blow the APEX.
I'm in the same dilemma, but rather than find that long cable, I'm repositioning my head unit to see what I can do with it first.