Try Amazon, Ebay, Rock auto, Autoplicity, Autozone, Napa, etc. Take measurements, and is it pressurized? (Radiator cap)
You may have to adapt a slightly different one, make brackets and put on different liquid fittings, BUT it won't be 900!
2015 Fleetwood Discovery 40E on a Freightliner XCS chassis with a Cummins ISL9 pulling 1 and/or 2 motorcycles, '07 Honda Accord OR a 17' Runabout Boat.