Twice a year we have a big collecting fair in Utrecht. There you can exchange or buy every conceivable thing you can imagine. I still have a little collection of some slides and calculators as seen above.
and have used them in the early days of my profession. As the black one before the printed sheet on the first photo. It could multiply, divide and making cubic content calculations. Of course there is a lot of other stuff (photo impressions). You name it and it is there.
This year it is held at 12 and 13 April here.