1. RetroSynth Website: The Regression FM soundfont was created by Plogue Art et Technologie and is available for download on their website. You can find it by visiting their website and searching for "Regression FM".
2. Loop and Sample Sharing Websites: Various websites specialize in sharing soundfonts and samples. Some popular sites where you might be able to find the Regression FM soundfont include Freesound, Loopcloud, Splice, and AudioZ.
3. Third-Party Sample Libraries: Some third-party sample library providers may offer the Regression FM soundfont as part of their collection. You can check websites such as SampleScience, Bedroom Producers Blog, and ADSR Sounds for their sample libraries.
4. Audio Synthesis Forums: Audio synthesis and music production forums like KVR Audio, Synthtopia, and AudioFanzine often have threads where users share and recommend soundfonts. You may find the Regression FM soundfont mentioned in these discussions.
Remember, when downloading soundfonts from external websites, always ensure that you're obtaining them from reputable sources and that you have proper security measures in place to protect your system. Additionally, some soundfonts may have specific licensing conditions, so make sure to read any accompanying documentation or license agreements before using them in your projects.