Here's a good site http://www.oldtimejam.com/Jam.html
Todd Phillips has book called
All Star Bluegrass Jam Along
It has 21 good songs to learn with music for bass and the melody if you reed treble clef.
There is a Real Bluegrass Book but I personally think they've made the charts too complicated.
This user run app will play the chords and you can remove the bass part http://www.irealb.com/forums/forumdi...egrass-Country
The best thing may be to pick up some Bill Monroe CD's and listen to them over and over. You should be able to sing the bass lines after awhile.
You gotta get used to the occasional crooked chord progression and the song that sits on a chord for a lot of bars then changes on a week beat.
A friend of mine that's a pretty good rock and jazz player got totally lost when he sat in on Mountain Dew which , if you know the song is pretty easy.