I make my own for my S gauge locos. This one here uses a 78L05 but I recommend a larger 1 amp 7805 regulator if using track voltage for the source instead of a smoke feature out of a TMCC board..
It has a resettable one shot timer so at faster speeds you get constant smoke and not a choppy pulse .
Also R-1 is optional if you want the fan to run at a constant slow speed at idle.
Remove if you don't want that feature.
Costs about $5 in parts. It can be made on a piece of vector PC board.
Carl