I think they get surplus from Fleetwood and Suncrest. Fleetwood has a big plant for motorhomes in Riverside, Ca. and Suncrest has a park model mobile home factory in Corona.
I bet there are more manufactureres down here than one could imagine.
Walts has a showroom inside with "new" OEM stuff, and then the back yard is organized chaos of take aparts. You can show them the most obscure little part and their part puller guy will know exactly what it is and where he last saw one.