I did a bit of digging.  Townsend Whelen wrote "In the Days of the Krag" and told of the Pennsylvania National Guard getting their first Krags in 1900.  That was the first time he saw the rifle.  Ned Roberts wrote that his NH National Guard unit got their first Krags in 1907. 

Individuals could probably get a Krag before 1914 if they were NRA members and members of a rifle club and team, or if they were politically well connected.  In 1914, Congress authorized the sale of Krags to members of the NRA via the DCM.  By then, there were enough 1903s in 30-06 caliber to arm the small Army, the Navy and Marines and some of the National Guard units.  Some sales were made before 1916 and the Army was sent to the Mexican border, but after that, with involvement in war at least a possibility, sales were stopped.

The 3rd Infantry Regiment of the Illinois National Guard traded in their Krags for Springfields early in 1916, just before they were sent to the Mexican border.  But some Texas National Guard units still had Trapdoors in 1917.  Not until after 1919 did the Army and National Guard make a concerted effort to get rid of the Krags.