Enter "Terry Pratchett-dark morris" on Youtube and there's not only a vid of a mixed group of aussie(!) morris dancers dancing the 'Dark Morris' but also another vid of another aussie group dancing 'Terry Pratchett's notorious "Stick and Bucket" dance'!

I seem to recall hearing an interview with TP where he mentioned being at a Discworld shindig somewhere and witnessing a group of morris dancers doing the dark morris. He was knocked out.