Other builders would probably be willing and/or thrilled to craft an instrument for you, to your specifications. e.g. wide fretboard.
I do not know if he's for hire or not, but if I were seeking a great instrument and wanted something custom, I'd check into this guy right here: http://www.everythingdulcimer.com/discuss/memberlist.php?mode=viewprofile&u=4808
Many others are available, but I think I'd at least see what that guy had going on. Look in the "Dulcimer Maker" forum and you'll find some photos of his work and how it goes together. I think he's in Maryland, but shipping is cheap enough these days.