Hi Aussie Bob
I'm pretty sure that you will have tried anything that I might think of

Still, just in case, have you looked at Thomas Buxton/Buckston's will? I just wondered if he passed the scrap(s) of material on then... too handy to be true no doubt. In any case it would be good to see who got a mention.
I tried making a time line. Your Thomas went to Tasmania in 1821, with the tartan? He was born in about 1791 so he certainly acquired the tartan after that date, either a gift or a bequest. Cullodon was in 1746 so if Thomas Buckston gave the tartan away (rather than leaving it in his will) then it was probably to the generation before Thomas Buxton, don't you think?
I'm trying to imagine, if I had a strip of cloth, decided to cut it up and give it to family and friends, then who would I give it to? Siblings and cousins most likely. So the people mentioned in his will would be interesting. You can buy it online at
http://www.rootschat.com/links/0ebs/ , if you don't already have it.
The best list that I know of for parish records in Derbyshire is the one at the Archives here
http://www.derbyshire.gov.uk/leisure/record_office/our_collection/default.asp (scroll right down for the link to a pdf). Mayfield you have already looked at. That would be Staffordshire so the parish records would be here
http://www.staffordshire.gov.uk/leisure/archives/home.aspxAs you say, there is a lot not in the IGI. You probably know of this site
http://freepages.genealogy.rootsweb.ancestry.com/~hughwallis/ which indexes the submitted entries in the IGI, by county and parish.
If you haven't already seen it then
http://www.wirksworth.org.uk/MENU.htm has a section called Ince's pedigrees. It is not the most user-friendly index but sometimes it leads to gold. It is based on the notes made by a lawyer 1826-1860.
Looking at that, it seems to me that Edmund Buxton as a name has some connections to Fenny Bentley and that is not included in the IGi (except for a few years). Other than that, nothing really jumped out but I didn't look at every single tree

I'm not sure how realistic it would be to go through all the parish records for the area!
I hope that some of this is useful.