Check out this place:

http://www.folkcraft.com/
and go to the Dulcimer Builder's Supply page

You can get the wood you need - either in kits or rectangular pieces
palned to thickness.
You should DEFINATELY get a pre cut Fret board - the formula for the
measurements of the frets is pretty exact, and the boards come slotted
to accept fret wire

Give them a call (or email) and tell them what you want to do, -
they'll answer your questions and fix you up.

JD