The book should be available (so that those with historical interest can see what this kind of propaganda looks like & how it has been used), but any edition sold should have a long cautionary preface. Pretending it was never written doesn't help anyone.
I think it's a little different when a retailer that is primarily a bookstore sells it, because then it can make a claim that it is selling the book for historial interest, while not endorcing the content.
I bought "Mein Kampf," which sold a lot of copies in Germany, and Protocols, evil as it is, has been influential and helps to reveal the evil of anti-Semitism that has taken hold in the Arab mind.
Available?...yes in a library catalogued under "propaganda", not on a money making businesses website or store.