http://www.unfretted.com/loader.php?...ik_quartertone
Check above... I did a 'google' but didn't read the whole thing, he may be of some help.
If you are doing this for melodies and not for chords, you might try just removing the frets from a regular guitar and seeing what that does for you. (this would open up the world of alternate tunings and scales for you, assuming you are into that kind of thing)
If you are really into it, you might try re-fretting a guitar for quarter tones.... just put in an addtional fret between the ones that are already there. Actually a luthier could do that for you... it really isn't all that hard, you just have to have to tools to cut the fingerboard and install the frets.
One last idea. Re-string a regular guitar with the 'low' 3 strings a quarter tone below the 'high' strings. In other words, the top 3 strings would remain the same as always, but the low strings would be the same gauge, and tuned the same as the high 3, but a quarter tone off (sharp or flat, depending on your needs).
