A JVS Wiring Harness is a USB Cable.
if you're talking about the wiring between the JVS IO and the controls. really that's two parts,
1. control panel harness which goes from the control panel to a set of connectors specfic to your cabinet, many people make these. But it's control panel and cabinet specific
2. A Cabinet sub harness that connects the control panel harness to the IO board. These are cabinet specific and IO specific. AFAIK no one makes these, typically because these are considered part of your cabinet and it's not something that ever gets removed from the cabinet unless it was really badly gutted or modified. Nearly Every JVS IO board uses a different pinout; there's no standard for this.
Since you're building your own cabinet you might consider buying a complete harness from another gutted cab that's being parted out. That's what I'd probably do.
Alternatively the cheapest/easiest option would be to buy a JAMMA harness and run either a Sega JVS to JAMMA IO or a Capcom IO
or you could always just crimp together whatever harness design you want.