I'm not aware of any literature on the subject but the Combined Morris Organisation at http://www.morrisdancing.org/ might provide some leads and further reading.

We, The Powderkegs, know how OUR kit developed but that's probably not much use to you as an isolated example!

That's the correct phrase, by the way, 'kit', rather than 'costume' - a minor point but it might help with your enquiries.