There are still Markhams in the East Riding including one John Markham who is well known in art/local history circles, plus a flourishing family history network here. I live near Wressle so if you ever need a specific search I might be able to look. Will try to do a quick search in Goole local history library for relevant indexes if I get time in the next couple of weeks. The Harrogate Show may well have been the Great Yorkshire Show - in which case the Yorkshire Agricultural Society may well have records. It should be relatively easy to check whether it was held there that year. Unfortunately my blacksmiths are all in the south...Sales and Honeysetts and variants welcome!