The Dulcimer Shoppe (McSpadden) makes the McSpadden Dulcimer, and is possibly the most popular maker in the US for those who want something "a lot better than homemade." I don't know how readily they are available elsewhere; but I would expect no difficulty in getting one almost anywhere.

The other often cited "excellent" maker, Blue Lion, has been mentioned above. Samples I've seen are very good, but they seem to be a more "elitist" maker, with correspondingly higher prices. That may be only because they only show their "best" at festivals and shops where I've seen them. Those who have one are very proud of them.

The basic instrument is simple enough that a kit, or fab from a plan, is not difficult. Ideally, and by tradition, the player should make his/her own I suppose. The good commercial/artisan assembled instruments do tend to be better set up, and often include little "tricks" that are hard to match in a kit or "scratch" instrument. (I've built 3, including both kit and scratch, so there's some experience speaking.) More ordinary makers may be about what the average builder would get on a second or third kit, but may be perfectly satisfactory - or superb. (Homebuilds get better with experience.)

As always, taking a competent player along to give an opinion before purchase is an excellent idea where possible, but the selection should be based on the preferences and interests of the player who will use it. Dulcimists who stick with it tend to develop "idiosyncratic" styles that may make the "experienced choice" questionable, or overly expensive, for a beginner.

John