Good question - no easy answer, at least here in Colorado. Permits are available if you're lucky enough to live in a jurisdiction that grants them. I live in Larimer County and our current sheriff does grant permits. They are "statewide", however other local municipalities may or may not honor them. For example, the permits are not valid in the city and county of Denver.
It's not nice. Take a little drive across the state with your permit and you're welcome in one town and liable to be arrested in another.
Every couple of years there's an initiative to get a consistent, genuinely statewide permit system in place, but we haven't succeeded yet.
Upshot is, check the rules where you live, and wherever you plan to travel, and like most laws, pleading ignorance won't work.
As a side note, I took a training class to meet the requirements, and it was taught by a local police chief. He made a couple of interesting observations with regard to this. Since it is not consistent across the state, it also means that law enforcement across the state has different ideas about what they are supposed to do. He said if you are pulled over for a routine traffic stop in Colorado, you are not obligated to answer if the officer asks you about weapons in the vehicle. Nor are you obligated (unless you're being arrested anyway) to let them search the vehicle. Best policy is, "Don't ask, don't tell", so to speak. Second best option is to prominently display your permit alongside your drivers license so the officer is aware as early as possible that you are a "good guy", and is hopefully put at ease.