This is a link to the National Adoption Information Clearinghouse website:
http://naic.acf.hhs.gov/
It will take you directly to the search page that will give you several options in looking for adoption resources specific to your state, including agencies. This will be a good place to start in your search for agencies. I don't think it is an exhaustive listing, so check for other resources also. You can also click on HOME and search around the site. It's a very good source of information.
Best of Luck