Representatives in Congress and the Senate screen electronic contacts to be from their Constituents - including the Leadership. As a result, you cannot contact representatives other than your own with Countable.
The best way to contact a Representative other than your own is to contact them by phone. You can find contact information for all Members of Congress here.
Additionally, you can call congressional leadership at the following phone numbers:
House Speaker Paul Ryan - (202) 225-3031
Senate Majority Leader Mitch McConnell - 202-224-2541