Sorry for such a slow reply.My grandfather had to look out the information he had researched.The following are the sources he has come across re: The Mathers (in the Mearns in Aberdeenshire, Scotland making soup out of the town's sheriff!!
"Tracing Your Tartan Roots" in the August 1990 edition of the Scottish Banner.I believe it is a newsletter or magazine in Canada.
Also the story is mentioned in a book written by Nigel Tranter on Kincardineshire, Scotland.
Also try you could try the First Statistics of Scotland written in 1790.I believe these are published and accessible by the general public.
To prove that the Mathers descended from Aberdeenshire, Scotland was a "Kaim of Mathers" built which I believe is 14 ft high and is like a tower in Egglesgreig in the parish of St. Cyrus, south of Aberdeen, on the East Coast of Scotland.