Hi Grace,
Replacing a drill chuck is a simple repair if you first know a couple of tricks. We have prepared an article and video that will provide you with all of the information you will need to replace your drill chuck. You can find the article and video at the following link...
http://www.ereplacementparts.com/article/890/Cordless_Drills_101.html
There are no separate repair parts for the chuck itself. You will need to replace the entire chuck. The chuck is part #390756-00.
I hope this helps you with your repair!
-Mark