I'd like to say that Diane in Chicago has a set. I'll check - WY
Yes, dulcimer books can be a solution to working with 3 string CBG, but you are going to run into a little trouble working with fret numbers. (Dulcimers have a limited diatonic scale as opposed to a guitar's chromatic scale)
In general, if you want to strum chords, the set up of a 4 string cbg is more applicable. For instance, tuning the strings like the 4 higher strings of a guitar, Dgbe makes it possible to play in a standard method. Just by tuning the high string down to d (Dgbd) you are now in open D tuning. Please see my page, I am currently blogging a series of lectures called Chord Chemistry 101.
I have an instructional video CD available on 3 string cbg that you might find helpful.
Due to the 3 string set up, it is easier to approach playing with the use of two note doublestops that are basically nothing more than fragments of chords. Also, tuning the first string differently will very easily change the whole open tuning offering more possibilities.
I hope you find this helpful. Please feel free to write, if I can answer any further questions. Enjoy.
Set of chord charts.