This thread inspires a couple of thoughts:

* Many French Canadian fiddle tunes have an "added" or "missing" beat; I initially found this very disconcerting after growing up dancing to contras tunes with a very square 32-beat A part and 32-beat B part. But after listening to more French-Canadian tunes, I find the unexpected rhythm to be a large part of their charm.

* I learned to dance zwiefachers from an old Folkcraft 78 record, which had only two tunes (one easier than the other, and conversely). More than a dozen zweifachers can be found in Peter Barnes' splendid collection "A Little Couple-Dancemusik" (1992). The book is available from CDSS at cdss.org, and is chock full of wonderful tunes.