That would be www.elderly.com . They do have most parts for autoharps, however they may not be able to get the parts for the truely old harps (black boxy things with the string anchors set under a plastic end piece, and the anchors themselves are pins set in the base of the instrument). Be advised that some parts are hard to get and frankly, unless you are planning to build some of your own chord bars, such as Bm, Em, F#m, etc. it is cheaper and easier to order the 15 bar (or 21 bar) adaption kit, which comes with all the chord bars, springs, and channels, etc. for about $80.00 dollars 'merican. Then you can save the working parts for replacements as they are needed. Be advised that the autoharp felts are going to black in the near future, and that 15 bar felt is an 1/8th of an inch wider than 21 bar felt (21 bar felt can go on 15 bar, but not the other way round.)Also get your strings from Elderlys as they are cheaper for mail order than anywhere else (A style are loops for the older harps mentioned above, B style have buttons on the end for the newer slotted end pieces - about $32.00 'merican). Good luck!
(As for the "What-harp", tell them that West Virginia is passing a bill to make it the State Instrument, and that it lends itself well to Scots-Irish Appalachian ballads and aires such as "Archibald McDonald of Kepoch" and "Teddy O'Neil".)