OpenSaberVR is an open source BeatSaber clone which supports the custom songs from the mod community of BeatSaber. It's still under development, but the first development snapshot has already a good gameplay and the mentioned support of the songs.

https://devplayrepeat.itch.io/open-saber-vr

Really love that you made it open source. Going to check out the source code in the meantime, but will definitely try out when I get my Vive setup again.