I've highlighted a few school Pro Days were Colts scouts have, typically, attended. From NFL.com:
Thursday, March 4 -- Baylor, Florida Atlantic, Missouri, Syracuse, Wyoming
Friday, March 5 -- San Diego
Monday, March 8 -- Central Washington, Utah
Tuesday, March 9 -- Auburn, Central Arkansas, Indiana, North Dakota State, N.W. Missouri, Oklahoma, Tuskegee, Virginia Military, Western Michigan
Wednesday, March 10 -- Brown, California, Colorado, Kansas, Kentucky, New Hampshire, New Mexico, Rutgers, Texas A&M, Washington
Thursday, March 11 -- Alabama-Birmingham, Furman, Idaho, Ohio, Stephen F. Austin
Friday, March 12 -- Eastern Washington, Jacksonville State, Michigan, Ohio State, Oregon State, Purdue, Texas Christian, Urbana
Saturday, March 13 -- San Diego State
Monday, March 15 -- Air Force, Albany State, Clark, Georgia Tech, Montana
Tuesday, March 16 -- Bowling Green, Delaware, Eastern Kentucky, Toledo
Wednesday, March 17 -- Arkansas State, Arkansas Tech, Hampton, Illinois, Marshall, Michigan State, Penn State, William & Mary
Thursday, March 18 -- McNeese State, Nicholls State, Temple, Virginia, West Virginia
Friday, March 19 -- James Madison, Minnesota, North Carolina Central, N.W. Louisiana, Tulane
Monday, March 22 -- Iowa, North Carolina A&T
Tuesday, March 23 -- Iowa State, North Carolina, Notre Dame, South Dakota State
Wednesday, March 24 -- Nevada, North Carolina State, North Texas
Thursday, March 25 -- Central Florida, East Carolina
Friday, March 26 -- Arizona State, Boise State, Miami (Fla.), Wake Forest
Tuesday, March 30 -- Houston, Texas Southern (at Houston), Texas State, UCLA
Wednesday, March 31 -- Pennsylvania, Southern California
Thursday, April 1 -- Hawaii