There is a museum on Cape Clear - they may help you http://www.capeclearmuseum.ie/
Also Skibbereen Heritage Centre nearby has a genealogy service. There is a tv documentary on Irish Tv about Cape Clear at the moment. You can watch it on rte.ie on the Rte player facility. It is in Irish (Gaelic) but is subtitled. It is called Ar An Oileain. Translates as On The Island.