Congratulations, Roberta!
I encountered a Musical Traditions cherry dulcimer while I was in college, and it looked and sounded just beautiful. I wasn't aware that there were any kits out there, but I would have snapped one up in a minute if I found one!
Good luck on your search. If there are any measured drawings of the parts, they could be reproduced fairly easily by a woodworker or luthier.
Burrell,
That's how I make wooden cases -- build the whole box, then slice off the lid. It'll fit perfectly every time.
I haven't made box joints at the corners, though that's the best way to fasten them.
I generally use either 3/8" solid poplar or 1/4"- 3/8" plywood for the edges, and 1/8" plywood for the top and bottom pieces.
I wrap the raw box piece exteriors with thin vinyl sheet goods, usually black, and glue/staple the edges all around.
Then the rigid-foam interior is added and cut to accommodate the instrument. The foam is then covered with Fun Fur or flannel material and trimmed. Sometimes I add a flap lid in one corner for an accessories area.
Then 3 or 4 small brass hinges are added, 2 draw catches and a handle.
Hi, all.
I've been warming up to poplar (so to speak) in the past few months. I know it has some bad qualities and is considered a junk or secondary wood by cabinetmakers, but it can make a FINE sounding dulcimer!
Ask Robin Clark, Ken Hulme, Elaine King, Kevin Messenger or others on this site. I was surprised myself when I first heard the sound of the firstdulcimer I made from poplar. And the color variations are interesting.
Gentlemen:
Looks 99.9% like a McSpadden Sweet Song assembled kit to me. I've built a couple of them, and they look JUST like this one. (Of course, the fit and finish on mine were much better! 
).
