Some suggestions based upon my own experience.

Bill Taylor - web.utk.edu/~bt1/default.html. My wife owns one. Several of my dulcimer playing friends own Taylors. One friend owns five at last count. I've always been impressed with Taylor dulcimers. Some have even excited me. Some have the sort of tone and volume I think you are looking for.

Jerry Rockwell - www.jcrmusic.com/index.html. Several dulcimer playing friends play Rockwells. To my ears, the sound is not as consistent as with the Taylors. Never played one that excited me, but their owners love them. He makes them in all sizes. Some can be quite loud.

Incidentally, the luthier who made my dulcimers, big beautiful ones which have the volume, sustain, and tone necessary for jamming with guitars, does not make them any more.