I've had luck with
www.marinco.com when looking for a new battery chassis disconnect switch. Of course I had to call the Freightliner help line and give them the last five digits of my VIN so they could find the part number.
Some items are OEM {Original Equipment Manufacturer} which means even calling GE would be of no value as they may make that contactor specifically for a manufacturer and don't actually have rights to resell it. If it's not OEM,
www.grainger.com has a wide variety of contactors; you'll need to know the amperage rating and coil voltage which are typically written on the side of the contactor.
Good Luck & Hope I've Been Some Help!
P.S. "RV Wizard" & "007" members here in IRV2 seem to be a wealth of knowledge and internet links.
Chris & Marily