I would like to buy facebook pages and groups. Does anybody know for any good source.
No idea. I thought that was against FB's TOS
IIRC (from the last time a similar question came up) you have to have Facebook's prior consent to transfer ownership.
Transferring ownership is one thing... selling a group?
I would still recommend reading their TOS carefully. You don't want to get into trouble
We have had two recent threads on the subject (and quite a few older ones, too):
You can contact page/group admin to buy their pages or groups.
Many people selling this type services. Find on Facebook.