I think it's great that you're starting on this early! That gives you plenty of time to get the skit prepared, and allow kids to rehearse.
I searched Google for "Thanksgiving skits" and came up with the link below. It contains quite a few free-to-use skits. Some are unique, funny, more modern Thanksgiving skits, while there's one link to the classic "First Thanksgiving" skit.
You might also try checking out kids' books about the First Thanksgiving from the library, and encouraging the class to write their own skit (with teacher or parent help, of course). It could be a fun way to get them thinking creatively, and to make sure everyone gets a substantial part in the play.
I'm also including a link to our Thanksgiving portal below. It contains a slew of Thanksgiving activities, printables, articles, and book recommendations. You may be most interested in the do-it-yourself decorations for the play, as well as the homemade Pilgrim and Native American costumes that can be found in the activities section.