Glenn Beck’s The Blaze kept a count:

Several GOP senators joined Paul in his
crusade, however, many others didn’t and were not in attendance.
Further, very few Democrats participated.
The Republican senators who
participated in the filibuster with Paul include, Sens. Ted Cruz
(R-Texas), Marco Rubio (R-Fla.), Mike Lee (R-Utah), Pat Toomey
(R-Penn.), John Thune (R-S.D.), John Barrasso (R-Wy.), Tim Scott
(R-S.C.), John Cornyn (R-Texas), Jerry Moran (R-Kan.), Ron Johnson
(R-Wis.), Jeff Flake (R-Ariz.), Mitch McConnell (R-Ky.) and Saxby
Chambliss (R-Ga.).
It should be noted that Sen. Mark Kirk
(R-Ill.) was in attendance and supported Paul’s filibuster by bringing
the senator a thermos and an apple, a likely reference to “Mr. Smith
Goes to Washington.” However, Kirk, who recently returned to the Senate
after suffering a stroke, did not speak during the filibuster.
There are a total of 47 Republican
members of the U.S. Senate, meaning 32 other GOP senators sat out the
filibuster protesting the federal government’s controversial drone
program. To find out who those senators are, comb through the full list here.

Breithart’s news site actively counted the list of who did not attend:

Alexander, Lamar – (R – TN) Class II
Ayotte, Kelly – (R – NH) Class III
Blunt, Roy – (R – MO) Class III
Boozman, John – (R – AR) Class III
Burr, Richard – (R – NC) Class III
Coats, Daniel – (R – IN) Class III
Coburn, Tom – (R – OK) Class III
Cochran, Thad – (R – MS) Class II
Collins, Susan M. – (R – ME) Class II
Corker, Bob – (R – TN) Class I
Crapo, Mike – (R – ID) Class III
Enzi, Michael B. – (R – WY) Class II
Fischer, Deb – (R – NE) Class I
Graham, Lindsey – (R – SC) Class II
Grassley, Chuck – (R – IA) Class III
Hatch, Orrin G. – (R – UT) Class I
Heller, Dean – (R – NV) Class I
Hoeven, John – (R – ND) Class III
Inhofe, James M. – (R – OK) Class II
Isakson, Johnny – (R – GA) Class III
Johanns, Mike – (R – NE) Class II
McCain, John – (R – AZ) Class III
Murkowski, Lisa – (R – AK) Class III
Portman, Rob – (R – OH) Class III
Risch, James E. – (R – ID) Class II
Roberts, Pat – (R – KS) Class II
Sessions, Jeff – (R – AL) Class II
Shelby, Richard C. – (R – AL) Class III
Vitter, David – (R – LA) Class III
Wicker, Roger F. – (R – MS) Class I