PeterH:
How long do you need to operate it for? I'm no musician but I've seen them played and have the impression they need quite a bit of pressure - probably several PSI - which would be hard to generate from a fan. I suspect you could operate it from a balloon for several seconds if you wanted to try that to prove the principle - then your problem would be how to get a pump/fan to generate similar pressure at the required flow rate.
Best case scenario I'd need them to play indefinitely until I turn them off myself. The recorders I have made are of a small scale and require less pressure than regular wind instruments. I am tempted to try out the mini air compressor like this
www.google.co.uk/products/catalog?hl=en&client=firefox-a&rls=org.mozilla:en-US:official&channel=fflb&q=mini+air+compressor&bav=on.2,or.r_gc.r_pw.r_cp.r_qf.&bpcl=38625945&biw=1846&bih=987&um=1&ie=UTF-8&cid=5286243728415743297&sa=X&ei=YrCqULPdO8a90QWZh4CYAQ&ved=0CH0Q8wIwAw
it produces up to 250 psi so it is strong enough. It might be too loud and I am not sure if I can find a good way to control the pressure of air that it produces.