Call or Visit a Manufactured Home Dealer for a list of lots or land for sale.
Do a search on Google: Manufactured Home Dealer
The ones I know of are Age 55 + communities.
Although some of information is on the Internet.
The best way to research is to visit the City Planners and view the zoning maps usally hanging in their office.
Ask the Planner what areas allow mobile homes on unimproved or improved land/lots.
In Areas of the County, contact the County Planning Departments, ask for Current & Future Zoning Maps. Each City has a Planning department. Maps run $40 ++.
Also go to the City & County Building Departments, Code Enforcement, & Water Departments and ask for print outs or regulations regarding mobile or manufactured homes in parks, raw land or improved Lots. You can check online first.
Try to talk to the City or County Employees, they are a wealth of information.
cell or text: 909 800-0650
Still, as Terry suggests, if there are any, a local Realtor should be able to help. As you probably know, though, most mobile homes aren't listed on the MLS because the homes themselves are often sold by the owners, and the homes are titled through the DMV. Where I am, I'd say maybe 15% of the homes appear on the MLS; the other 85% are sold privately. I'm sure that number varies geographically.
One other possibility is to call the managers at various parks. Even though they probably don't sell the lot with the home, they probably are aware of any nearby parks that do.
Hope that helps.