Your Röwa Y6b was manufactured in the mid 1970´s by the long defunct Röwa Co. in Germany. The smoke generator in it was supplied by Seuthe in Germany, who do not stock spare parts for it anymore.
I am afraid you will have to live with that smoke unit being out of order.
Does anybody have any info on the wiring and testing of the Rowa 2-8-8-2 smoking units for n gauge I have a couple of these units and want to find out why the smoke units won't work and how to test them and replace parts if available. Thanks in advance.