The site is Congress.org, you can contact any Federal agency, Congressman or Senator along with your local officials through this site.

You can request your message be sent as an email or letter and you can request a reply to your message (I'm not saying you'll get one from the BOP). I have sent letters to my Congressman and I have generally received a reply, a form reply but a reply nonetheless.

http://www.congress.org/congressorg/dbq/officials/agencies/?id=4278&dir=congressorg&command=depresult2&submit.x=4&submit.y=15