From the Congressional Yellow Book, Spring 2007:

National Republican Senatorial Committee ("purpose to elect & re-elect Republicans to the Senate")
Phone: 202-675-6000
Fax: 202-675-6058

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Office of the Senate Minority Leader
Phone: 202-224-3135
Fax: 202-228-2574
Chief of Staff: Kyle Simmons

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Senate Republican Policy Committee ("legislative and research organization serving all GOP Senators")
Phone: 202-224-2946

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Senate Republican Conference (Jon Kyl, Chairman) ("mission of the Conference has expanded and been shaped as a means of informing the media of the opinions and activities of Senate Republicans")
Phone: 202-224-2764
Fax: 202-228-4276