A low power home brew unit for smoke , though likely anemic in production should be pretty easy. I've seen single AA battery toy trains that puff smoke, and run for hours. The fluid is a water and vegetable oil solution, the element is a single delicate nichrome wire, the puff by bellows on a cam.
Duel batteries, or super cap and battery? Battery in cars for long haul, super cap/small battery in the engine for run arounds, etc. where power use is much lower, might be a feasible combo. Tethering by truck/ wheels/ track and isolated couplers, maybe body mounted KD? This could allow many battery cars to charge, say on a 3rail siding, full charge cars connected by switching in a new car, and dropping the empty prototypically. Still plenty of room in the loco/tender that way for sounds etc. A cap should be able to smooth the iffy connection from the couplers, the loco recharging off the cars as needed during running.
Regulating voltage, the cars might be 24v, the loco 12v making recharge in the loco fast and full.
(Still gripping my plastic throttle 
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