I managed to find the install files here:
https://flirc.io/nightly/Flirc GUI/
For Windows, download FlircSetupNew.exe (which is v3.25.3-16-g28e801). To update to the latest version, download Flirc-3.26.3.tar.gz (or whatever the latest version is) and extract Flirc.exe and flirc_util.exe to where you installed Flirc.