One of the Forum's advertisers - DCC Supplies - sell a variety of Seuthe smoke generators. They have pictures on their web site. If you view enough pages on the Forum, there banner ad will appear and you can click through to the DCC Supplies site where you can view more information and place an order.
You have a couple of choices to make. The first should be easy enough since you can do it "on sight". This is to choose whether you get one which has heat insulation around it and a narrow top or one one which is uninsulated and is a straight forward cylindrical shape.
The second choice is the operating voltage. The more commonly used type works at a lower voltage but takes a higher current. The second type has a higher voltage but takes a smaller current. The total power used (current * voltage) is the same for each model. Tests I did recently indicate that the minimum voltage really means what it says. If you don't reach those volts, nothing happens; so if you're maximum voltage is 12v and you pick the low current 16v version, you won't get any smoke.
You should only choose the low current version if you are using DCC and have a very low current "budget" for accessory outputs. Most OO/HO decoders have up to 500mA available, so unless you are using incandescent lamps as well, the higher current, low voltage will be fine.
The situation for DC is a lot less critical, but I would still go for the low voltage model.
David