[michaelsbradley]

They were never actually for sale. The practice of attaching a fixed amount of charitable giving to some indulgences, as the requisite good work for gaining the indulgence, was widely abused, to the point of great scandal, during several troubled centuries in the first half the second millennium. Given just how great the scandal was, following the Council of Trent, Pope Pius V abolished (1567) all indulgences of that kind and forbid any of that kind from being granted in the future. That disciplinary restriction is still in effect today, and probably for the best. Both prior to the centuries of abuse and afterward to the present day, the vast majority of indulgences were and are attached to certain prayers, occasions, and pilgrimages.

For more information, see the Indulgences[1] article in the 1913 Catholic Encyclopedia.

For the disciplines in effect at present, see Pope Paul VI's 1967 Constitution Indulgentiarum Doctrina[2].

[1] http://www.newadvent.org/cathen/07783a.htm

[2] https://w2.vatican.va/content/paul-vi/en/apost_constitutions...