so in plaza garibaldi in mexico city you can cruise by in the evening and see what the mariachi market has to offer. here, the mariachis from all over gather around, and kind of like the home depot parking lot is to day laborers, here they offer their music services. you can also drink there, unlike anywhere else in the city, which is a major plus. so if you hear what you like, you can take them, or give them an address or whatever. i can imagine the poor fool "dammit! my wedding band just canceled!" and then you go to plaza garibaldi, problem solved.
i imagine some sort of violent musical feud between rival mariachi gangs. smashed bloody instruments, would make a good movie. in reality though, it's more of a horror genre that quickly turns ugly. the mariachi can be aggressive, and as they can also be expensive (mariachi is actually a luxury good) so you can get yourself into trouble if you're not careful.
and if you happen to be driving by, roll up your windows! they actually swarm vehicles like in a zombie movie and will try to play to you inside your car. it's el mariachi! step on it! don't worry if a mandolin guy rolls over the hood, we've got to get out of here!