Thanks to this forum for the education of the existence of this set. It holds a special place in my heart. That is, despite me being an American who never set foot on a passenger train until I was 14. I like to think if I did live in that time and place, I would have gone nuts for this promo.
If I wanted to collect a stamped train ticket or the book they came in, what would I look for?
Much congratulations my friend. This is truly a special set and it is great to see you complete it. I have only come across the Pokemon Pouch and Pokemon wallet that was available during the promo as something to aid you in this promo run. I have seen the stamped booklets but only in blogs and never for sale.
But you can refer to this thread which might be useful
One of my favourite sets that got me into collecting Japanese cards in the first place! There are passport books that go on sale, a long time ago I got a stamp book for the Mewtwo/Eevee campaign. It’s a really cool artifact