As far as I know there has never been a problem in obtaining thermostats for the Cleveland, meaning those being manufactured with the “hat”.
The problem has been obtaining a “high flow” thermostat, with hat, for the Cleveland, which was the style originally used by Ford.
After Flowkooler stopped making their “hatted” high flow version, Marlin was the first to meet the demand for the correct high flow style of thermostat, which he created by machining the hat and attaching it to a high flow thermostat.
If you do not know the difference between high flow and standard flow I’m sure a search of this forum will find comparative photographs in more than one of the multiple threads on this issue.
Larry