Is there a central source for shape files for real estate across the US. Most counties will provide shape files via the county appraisal district. But there are over 3,000 to request.
No, realtors and real estate professionals typically covet their data and are very unwilling to share. To that point, my experience with the industry allows me to say that if these shapefiles did exist, they would be outdated almost immediately because people in the industry create new neighborhoods to make sales.
To your question, what is in a real estate shapefile? Neighborhoods? Zoning?
Zillow has neighborhood boundaries which is about the closest thing you are going to find.