Is it just me, or is the solution not to add more chargers, but to add more cables connected to a single charger, and have it round robin charge all the attached vehicles throughout the day?
You could also have the amperage be higher for the first hour or so of charging and then have it drop down over time or as demand increases.
I'm not aware of any existing chargers that would support this. There isn't much innovation or price competition in this space. It sounds like a great opportunity for someone to come in and do it right.
Relays attached to extension cords cost effectively nothing.
The idea of sharing a charger over a larger number of cars sounds much closer to the latter idea than the former.