Back to a bus tour idea - and I do hesitate to step in here because I am a comparative outsider to this group
I went with my Mom on a couple of lengthy bus tours - and they were great - all one had to do was pay and show up! There was a schedule that was fairly closely followed, so we knew what to expect.
Anyway:
Say someone in St. Paul, Minnesota has a huge collection - everyone - including the Minnesota person would gather at a central location - wherever they could get on a tour bus.
The first stop could be at the Minnesota collection - all the collection owners would have their stuff ready to look at -
then a couple of shops - then the next stop could be in Madison, Wisconsin - the next stop could be near Chicago
however it would take to loop back to St. Paul.
Depending on where the collections were located - and how long one wanted to spend looking at each collection - it could be doable. No one would have to bring anything because all the people would go to where the machines were located. If someone is a specialist about a certain type of machine, a lecture/demo could be scheduled - with an alternative shopping or activity scheduled nearby.
The bus tour place could help set up the itinerary and costs.