Correct me if I'm wrong but here is the contact info I found for Senators on the fence according to the homepage.

Hagan, Kay R. D NC
B40A Dirksen Senate Office
Building
Washington, DC 20510
P: 202-224-6342

Specter, Arlen R PA
711 HART BUILDING
WASHINGTON , DC 20510
TEL: 202-224-4254

Hutchison, Kay Bailey R TX
284 Russell Senate Office Building
Washington, DC 20510-4304
202-224-5922
202-224-0776 (FAX)
202-224-5903 (TDD)

Conrad, Kent D ND
530 Hart Senate Office Building
United States Senate
Washington, DC 20510-3403
Phone: (202) 224-2043
Fax: (202) 224-7776

Begich, Mark D AK
825C HART SENATE OFFICE BUILDING
WASHINGTON DC 20510
DC Phone: 202-224-3004

McCaskill, Claire D MO
United States Senate
Hart Senate Office Building, SH-717
Washington, D.C. 20510
(202) 224-6154
FAX (202) 228-6326