For classroom and practice, you might make do with less than a "complete" dulcimer. A "practice dulcimer" is almost trivially simple to make, although a few simple tools make it much easier.

The essential feature is a straight board, with bars (nuts) at each end to support the strings, and frets properly spaced for the notes. and some method to apply and adjust the tension of the strings for tuning, and of course, the strings.

The "box" on which the finger board is usually mounted would help to produce a fuller, and louder, sound; but the "strung finger board" alone, laid (or clamped) on a hard surface such as a table top or desk top, should be loud enough for practice. For easier handling, the simple fingerboard might be glued or stapled to a thin plywood or even stiff cardboard with a "dulcimer shape" to provide better simulation of the "feel" of playing a more finished dulcimer.

Early dulcimers were made with baling wire, staples, nails, and other "found materials" for the frets, although "real fret wire" would greatly simplify making "consistently alike" instruments if you plan to make a half-dozen or dozen at a time.

While it's possible to "hand whittle" tuning pegs, this is a rather time-intensive process and demands significant learned skills. If possible, "junk" geared tuners would make for quicker construction. If you want a "double course" front string, you would want four strings, so "half a mandolin" (one four knob tuner strip) would be convenient. If three strings suffice, half a guitar would work. You might find an instrument seller - especially one who does repairs - willing to donate a few "used" tuners, or sell them fairly cheaply if that's manageable with your resources.

Dulcimer strings are pretty well standardized; and "real strings" would be ideal; but used (donated?) strings from other instruments might be sorted to pick usable sets. Within limits, strings of "the wrong size" merely require more or less tension for tuning, but a significantly higher tension will make fretting (noting) somewhat harder, and too low a tension will give a "flabby" sound.

Several good resources have been suggested by others above, but for best results here being a member may be a significant help. The membership is free and requires only a real name, a name you want to use here, a password you create, and an email address. All info you provide is confidential, and the email address is needed so that the mud elves can send you help if you forget your password or have other site-related problems.

Members can send "PMs" (Personal Messages) to each other - not seen by any others, allowing you to choose whether to give someone an email addresses or other personal info "in private" and only to the individuals of your choice. Email is a main method here for trading pictures, sketches, and "extended details" for projects such as yours, since the site doesn't accommodate "art work."

John