They did. The 1903 Militia Act and the 1903 War Appropriations Act tried to regularize the state militia system , equip the state units with up-to-date rifles, and encourage civilian marksmanship. The Militia Act created what is now the National Guard, replaced the Trapdoor rifles they had been carrying with the new 1903 Springfield, and the War Appropriations Act started the Civilian Marksmanship Program. In the 1920's the CMP worked with the NRA to "sporterize" ( cut down and modify long military rifles into sporting rifles) obsolete Krag rifles which were then sold to the NRA membership at a modest price- perhaps $2. This was done again after WWII, using the Model 1903A3 Springfield Rifle, and after the adoption of the M16, the CMP began using Garand rifles: that program continues.

The 45-70 Trapdoor rifles that were obsolete in 1903 were also released onto the civilian market, and for decades were a familiar fixture in almost every small general store in the country: well into the 1940's one would be found hanging up behind the counter, usually with a $1 price tag.

The US government also supplied / sold obsolete arms and ammunition to various countries after WWII, at least in Latin America, the Caribbean: but someone else would have to speak to that.