Ivor Darreg stands as a shining example of how to create hand-built
instruments on a shoestring, and produce vividly memorable microtonal
music.
Jeff Scott also stands as a shining example of how to create vividly
memorable microtonal music, albeit in a different way with software
instruments.
All Bart Hopkins' back issues of the journal Experimental Musical
Instruments are still available from Bart himself.
If your interest centers around acoustic handbuilt instruments, also
try getting in touch with Buzz Kimball and visiting his workshop.
Ditto Skip LaPlante, who has 2 CDs out and gives regular performances
the New York city area using handmade xenharmonic instruments.
Building instruments yourself is probably a lot better idea and far
cheaper than buying 'em. I built myself a replica of a harmonic canon
correcting Partch's grossly incompetent design and it works and sounds
great. You can great a whole lot of microtonal music even with such
simple and easy-to-build acoustic instruments.
Bill Wesley in San Diego may be the current king of home-made
xenharmonc instruments, though Tom Nunn in San Frqancisco is no slouch
either.
Richard Waters continues to produce impressive metal-sculpture
instruments, as do the Baschet brothers in France.
As mentioned, virtually none of these people have any presence online.
They all inhabit meatspace, not cyberspace.