I would have thought that a clockwork motor would produce insufficient power unless you had a huge spring. Foot operated bellows similiar to those used for Harmoniums and Pianolas are would seem the best solution.

Most of the early church organs were powered by hand or foot operated bellows identical to those used for blacksmith's forges, but there was usually some form of air reservoir.

An uncle of mine used to pump his local church organ when he was a choirboy. If he pumped really hard he could completely fill the reservoir and a relief valve would open and produce a very loud farting noise - this was considered quite an accomplishment by the choirboys.