First, if the house isn't too old (maybe less than 30 years old), it's possible that a local real estate company might have the plans. The company I work for has multiple file cabinets full of the original developer folders/sales literature for thousands of houses/communities in the area. I wouldn't be surprised if there are real estate firms in your area that have the same collections.
If work was done on the house that required permits, it's possible that there would be architect's drawings of at least the area worked on at your city/county office that handles permits and inspections.
Another way--if it's in a community with similar houses--is to ask others in the community if they have the developer's sales literature. Lots of people keep that.
Hope that helps.