Sound Forge is pretty much the only software that can work with .sfw files, which are actually the projects made and saved using that software. As for sfw to fla conversion, this certainly related to export of the sound / audio content to FLAC format, which is supported in Sound Forge.
If you got .sfw files from someone, you can either ask them to do the export for you, or download trial version and see if that works out for you.
Updated: September 25, 2023