Hi,
Are you talking about the power supply or the cable? Power supply will be available from an Epson printer seller, and would cost around USD 180 when last purchased. I got my last one via Micros Hardware Support. There are cheaper places than them. They are considered consumables, so any place that sells Epson printers will be able to order a supply for you.
If you need a new Serial cable (DB9 to DB25) then most computer stores sill have one. Or is it another kind of adapter?