[MMM]

In my experience it really depends on the size of the festival, and how urban it is. For example, one local festival I went to every year (two small cities join together at one festival) event had grandfathered "yatai" (food booths) for decades. One family I knew didn't even WANT to keep their spot at the festival, but felt an obligation, as their family had been doing it for decades, and if they stopped for a year they would lose the spot permanently.

On the other hand just a couple train stations down was a yearly local festival (more of a parade, actually) where the parade went down the neighborhood's shopping street. If you owned a shop on the shopping street you could sell whatever you wanted in that space. If a shop was closed down, and no one cared, you could set up right there. I saw 10 year olds selling beer out of a tub of ice to all the dads (and some moms) watching the parade.

There is some sort of parade or festival in EVERY neighborhood, just about, so I would start by asking a neighbor "when and where are local festivals near here?" and then ask "How could I set up a stand?" If it is like my first story, then it might be impossible, but you might say "It doesn't have to be a big one." and find there are much more local events happening all around.