It is a PRK state law, so any and all LEOs in the state are charged with enforcing it.
There are two reasons it affects folks outside of the PRK:
- Anyone with an FFL is required to follow all laws in all of the states they do business in. So, they are required to observe laws like this or risk their FFL.
- Most business find that it's poor business practice to sell items to people that *could* get that recipient arrested and charged for a crime. It doesn't look good, and it's a further liability that they don't need.
However, non-FFLs that are out of state aren't in any danger (but the receiving person still is).
The violation is a "wobbler", meaning it can be charged as either a misdemeanor or a felony. Realistically, it's unlikely to be charged as a felony unless you are a known criminal or you get unlucky and someone is trying to score political points in their department and using your case to do so.
Also, most LEOs don't care about hi-cap mags unless you've otherwise done something to draw their negative attention. Once the mags are in the state (assuming you aren't caught receiving the package or driving them over the boarder), no one's going to be able to prove anything.