I haven't found an easy way to do this. I've had to go to http://www.house.gov/ and find each Congressman's home page. If you are going to send out a lot of faxes, you might want to first print out 2-3 copies of the letter so you can keep feeding them into the machine quickly. In the salutation, write Dear Representative_________:. In pencil, fill in a Congressman's name and fax the letter. Once the letter has been faxed, you can erase the Congressman's name and write in another. Doing this, I've been able to fax about 20-30 Congressmen in about one hour.