ACEC (National) has put together an online searchable Directory. Click on the below link to go to that Directory. If you need to contact ACEC directly, below is their contact information.
American Council of Engineering Companies (ACEC)
1015 15th Street, 8th Floor, NW
Washington DC 20005-2605
Phone: (202) 347-7474
Fax: (202) 898-0068