• Neighbors. You'd be surprised at how long some of your neighbors have lived in the neighborhood. If you're in an older home you might have a good chance of finding someone that lived there when it was built, or at least a family member that can help you find the original owners and/ or builders. You might also find a home in the neighborhood that looks very familiar. It may have actually been designed by the same person and could be quite similar in structure with a few differences in small details.
• Try a Realtor. Most likely if your house was build within the last 50 years or so (give or take a few years) a real estate agent might be able to help you find some of the facts about construction, or who the builder was. Many of them know the developers in the area and that could give you another lead.
• City Archives. Most cities keep archives older homes with pictures, building plans, floor plans, and sometimes even blueprints. Unfortunately many of these types of papers are not well taken care of and you may have to do some serious digging to find them. Ask the city if they have a local historian who can help you with finding what you're looking for.
• Maps of the neighborhood. You can also obtain from the city fire insurance maps of the area, most that will date back to the 1870's. How would a fire insurance map help you? Well, most of these maps will tell you what the house was originally built out of and will also provide a three dimensional drawing of your house in the neighborhood. Some are very detailed, while others are very vague. It's definitely worth a shot though.
•  Talk with a building inspector. Most cities require you to have a permit when you begin construction on a new home, and even when you remodel an older one. These plans and permits are generally found in the building inspector's office at city hall.
•  Find an architect or contractor. Most people think that an architect is used simply for designing new homes, but they can also help with figuring out how a home may have been originally built. They can come in and look at walls, windows, etc. and tell you if they have been moved or are original in their place.
• Look through plan books. There's a good chance that the blueprints for your home were taken from a pattern book. Many older American homes were built just like this and looking through some historic books can help you find a lead.
• Seek expert advice. It would be nice to say that if you put in all this work of looking for the blueprints, you will find them somewhere. But sometimes blueprints may not exist. Experts can help you try and recreate original plans and give you a better idea of how the home was originally built.

So there you have it; some ideas on where to get blueprints for a home that you're trying to remodel. And although it seems like this might be the most difficult part of renovating a home, it's just the beginning.