Because it is "abandonware," you will mostly find it on archive or enthusiast sites:
Documents folder, not the Program Files directory.: Real-time updates to 3D views as you adjust the 2D floor plan. Licensing and Availability 3d home architect deluxe version 30 free work download
Be extremely cautious of sites promising "free full versions." Many of these files can be bundled with outdated malware. Stick to reputable archive sites that specialize in preserving classic software. Unlocking Your Dream Home: A Look at 3D
You finally found a link, installed the software, but it crashes on startup. Here are the top fixes: Fix: Run as Administrator