There is no comprehensive list of bluegrass artists that make their music available for free, as of April 2015. However, there are many resources available to access royalty-free bluegrass music from various artists, including FreeMusicArchive, AccuRadio and Last.fm.
To choose the best resource, first decide how the music will be used. If the music needs to be downloaded to a device and played without an active Internet connection, then a database like FreeMusicArchive is ideal. This website offers a large index searchable by artist, album, song or genre, and every track can be downloaded by clicking the arrow on the far right hand side of each listing.
If a high-speed Internet connection is available in the intended venue, a streaming music provider like AccuRadio may be the best option. This website allows music to be played instantly without the additional step of downloading, and unlike many Internet radio services, it allows for unlimited skipping of undesired songs. The disadvantage of this option is that the database is only searchable by artist and genre not by album or track, and occasional advertisements are interspersed in the continuous music stream.
Last.fm occupies a middle ground between the two and functions both as Internet radio and music database. All the tracks on offer can be both streamed or downloaded. The tracks are either royalty-free or available by purchase through Amazon's digital download service.