Marcel Models in the UK stock a kit for making an 8-note organ out
of paper and cardboard.  By the description it plays from a roll
you punch yourself:  http://www.marcle.co.uk/catap55.html

This is probably not robust enough for Mark's purposes (I have some
experience of 5-year-olds!) but it might give a few ideas.

I did think that maybe visitors to the museum could purchase a kit
to build there and then take the finished organ home with them,
but at 22 pounds sterling (plus postage), it's not cheap!

Mark Williamson, now at Evans Head (just up the road from Woodburn)
New South Wales
Australia