If you mean running the fans in 240vAC, Comair Rotron make fantastic fans for this voltage. If you mean a regulator circuit and any old 12vDC fan, sorry for misunderstanding.
I'm open to whatever solutions might be available, and these guys look like they make awesome fans, but I think I need something much less awesome and more integrated.
Basically, I just need a 120mm PC fan, supply it with the right voltage, and thermostat.
In that case, I'd probably be thinking of a standard power supply with molex output (they make bricks like this) for a 5.25" fan controller that ties in thermistors on the control side of the equation. I know that's not the typical, "I just use a raspberry pi and..." answer we're used to here, so take mine with a grain of salt.