This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
The AY-5-3600 PRO keyboard encoder is not easy to find, but it can be replaced by the KR-9600-PRO keyboard encoder. The 9600 IC has more features, such as the bounce fix. I have installed one in my IIe and it works fine. By: Alberto Cavalcoli