“I would like to see the states pass laws to grant free national carry permits for all honorably discharged veterans, saying that they are members of the state militia and are on duty whenever they are carrying a weapon”.
State laws would need modification to set up the militia. As of now in most states the militia might be authorized by state law but in the majority of cases, the National Guard has usurped the militia’s standing. So in every state to my knowledge the unorganized militia does not exist.
In addition since 45 is the upper age limit mentioned in US Code, it would be of limited value as a twenty year retirement would leave a veteran with just a few remaining years to enjoy the permit. I do like the idea of the free permit for military retirees, but should probably to be fair include retired law enforcement folks as well.
https://www.law.cornell.edu/uscode/text/10/311
If the state law defined people veterans who carry as members of the militia, that is all that would be required.
The federal government can define militia for purposes of duty in the federal government; they do not have the power to define who a state says qualifies for the militia.
About half the states already have state military units outside of the National Guard.
https://en.wikipedia.org/wiki/State_defense_force