There are a lot of texts which are not available online, of course; there are only so many hours in the day. Conrad presumably already knows about the best online resource, the Traditional Drama Research Group, but I'll mention it for the benefit of others who may look at this thread. There are no American texts there (though there is one from Newfoundland) but there may be helpful references. Certainly there are a number of unpublished theses listed from American universities, some of which may deal with the tradition as it was found there.