Google Mc Calls,Simplicity etc and then put bell bottom pants in their search engine.Otherwise,check some of the thrift stores around your area that sells patterns.
Kathi

http://vintagepatterns.wikia.com/wiki/Category:Bell_Bottoms

The above link will take you to a list of vintage bell bottom patterns by manufacturers. When you click on a specific pattern (for example Simplicity 6370) a photo of the pattern will open in a window; below the photo look for a description of the pattern.

Then below the pattern description look for "Sources/Vendors" for a link to the vendor selling that particular pattern.

NOTE: I CANNOT AND DO NOT VOUCH FOR THE VENDORS. I simply pass on this website as an online source for vintage patterns.

If you have a bit of time to get it done, you can look for 'bell bottom' or 'flared' pants patterns on eBay. I get many of my patterns there. Shipping times vary with vendor and whether or not you "buy it now", or bid. How old is your daughter and/or what size is she? Maybe someone here can send you a pattern copy.

Here is a link that might be useful: bell bottom patterns