Do Christians have a particular duty to adopt?

Berean has a ministry named “His Kids” which deals with adoption:

http://www.bereanbaptist.com/ChildrensHKA.aspx

Also, Berean’s Foundation (the endowment fund) offers grants to help families cover the costs of adoptions:

http://www.bereanbaptist.com/Foundation.aspx

There are over 60 kids right now at Berean who have been adopted.