I was misunderstanding you originally. Yes, there are class 15 machines out there for treadles, though they're not as common as 66's or 27/127s. Here's one semi-local to me:
http://madison.craigslist.org/atq/3354418702.html
and another:
http://madison.craigslist.org/app/3342942722.html
Then again the same search probably netted 10-15 27/127 class and 6-8 66s so at least around here they don't appear to be common.