As a current owner (no pun intended) of an eMotorWerks charging station connected to a NEMA 14-50 outlet, I can suggest that your searches may be missing a few locations.
From their web site opening page:
Take JuiceBox along with you. All JuiceBox EV charging stations use
standard outlets and don’t require expensive, hard-wired
From the same web site, one can purchase adapters if one is in a situation which requires an adapter in the other direction. Their adapters allow you to connect the NEMA 14-50 into dryer and general household outlets (110v only).
Our JuiceBox 40 was purchased without the wifi option and I would have liked to have the ability to monitor the usage. With a 40 amp charge level, the vehicle charges faster than the computer forecasts, leaving us in a guessing game with how long it takes.
The lead from the outlet to the EVSE is rather short, but should not pose a problem with portability.
I think my lead might be a bit longer, as the unit is a year old and not as prettified as this newer model. It's just an ordinary weather sealed brushed aluminum box with wires, no lights, bells or whistles. I had inquired about a trade-in for the wifi version but the exchange rate convinced me otherwise.
Most (all?) US campgrounds which provide electrical service will have NEMA 14-50 outlets, making charging convenient in certain parts of this country.