EBay, Pianomart, or craigslist.
If it's a private sale, bring along an independent (certified) technician, unless you really know how to assess it yourself (hint: playing is just a small part). Make sure you hire a *piano* mover and not a general mover.
Last summer, I paid $3K for an immaculate Kawai KG-2C on EBay; it's probably worth three times as much. I'm getting a humidifier installed in a few months, but still pinch myself in disbelief.
Hmmm, in Russian a fortepiano is the instrument you can find on stage at a standard competition, and its related smaller instruments, like the KG-2C you just mentioned. Thanks!
But in English, the word fortepiano has come to be used particularly for pianos (original and copy) up to about the time of early Beethoven. Romantic pianos (those from about mid-Beethoven up to about 1900) can be called either way.
Therefore, keep in mind that when you say fortepiano, you are really making still too broad a generalization.
If you want a Fiorentine fortepiano (like Christofori's, good for playing Scarlatti and early Haydn, for example) you should get it from David Sutherland.
https://sites.google.com/site/davidsutherlandinstruments/reviving-the-earliest-pianos If you want a Stein or a Walter copy, to play mid-period Haydn, and pretty much all of Mozart, you probably should get it from the Harpsichord Clearing House.
https://www.harpsichord.com/...or if you are in Europe, you can go visit Paul McNulty, who will be your main source for several other pianos, like an Erard to play Chopin, or a Boisselot to play Liszt.
https://www.fortepiano.eu/Or perhaps you like to play Brahms, in which case a Streicher is what you need!
https://www.hecherpiano.com/verkauf_e.htmlNeedless to say, you likely will have to train a technician, and your PTG tuner may not really very familiar with these instruments at all. I had a self-touted expert tell me we needed to replace EVERYTHING in my 1873 Bechstein, simply because he had no idea how it worked or how to adjust it.
