I'm sure people more knowledgeable about this subject than I am will chime in with all sorts of ideas, but thought I'd mention a company I know of that sells such plays:
http://creativeeducationalsystems.com/
Click on "Plays by category", and scroll down on the right. You'll find Plays for the Winter Holidays near the bottom.
Hope that helps,
Michelle
(Disclaimer: I know the people who run Creative Educational Systems, though I make no profit from recommending them.)
