I just happened on this site today. http://www.realestateeconomics.com/floorplan.asp
I have not used their service, but it looks useful. The company based in SoCal, so it could have some good data for you.
If you are looking for a floor plan to build a home:
you can just go to google and search for floor plans. you can check out this one too.
You go to the city planning department in your city. Houses built after 1985 will be seen only on microfiche. If you know the address and APN number you can ask for to view it. Often this service is free of charge. If you know the builder's information you can contact and ask for copy of blueprints. You can also ask for the blue prints at the city planning department but you also need the approval signatures from the owner if the property is occupied by the owner and the from the builder as well before the city planning office releases the copy to you. It often takes about 5 to 10 business days. It depends on how busy the office is. I hope my answer is helpful for you.