NETGEAR ReadyNAS Duo v2 serial usb ethernet board

Netgear has never made parts available.  Your only chance is a "for parts or repair" system on eBay, and that's going to be quite a risk.  A system you at least know works would be better, especially since you don't need the power supply or caddies, which are often missing.  Just be careful of what you buy.  Many on eBay advertise a "DuoV2" that is really a V1.  Some V1's have a small v2 on a sticker that's different from a "real" V2, but those selling them aren't aware of the difference.  The parts are not interchangeable.  To make sure it's a V2, look for the V2 on the front and/or the large fan (almost as wide as the chassis) on the rear.

A working NV+V2 is another option into which you can move your volume.  Similar warning about a "real V2" applies.  A V2 is black and has an external power supply, while a V1 is silver and has an internal one.

BTW, what's not working?  If it's the Ethernet, it's likely not the I/O board that's the problem unless it's physically damaged, it's more likely the controller on the main board.