In short, you cannot get a fully functional, up‑to‑date, and safe copy of Source Filmmaker without ever touching Steam. The closest workaround is to install Steam on a temporary machine, download SFM legally, copy the entire SourceFilmmaker folder to another computer, and then run it from there. Even then, the copied version will not receive updates and may prompt Steam errors on launch unless you keep a minimal Steam client installed (logged out) or use a modified DLL.