This link might be useful to Fionn. I got it from http://web.ukonline.co.uk/martin.nail/Folkmus.htm - Martin Neill's pages - English folk and traditional music on the Internet - which says there's a folk club in Mansfield - "The Brown Cow Folk Club - but the link to it which he gives (http://www.sbarrier.freeserve.co.uk/) doesn't seem to work.

Whether that's any use for Irish sessions, I don't know - but if there are any existing or in prospect, those links should help winkle them out.