I see I forgot to give you the telephone book listings: In Sligo today are 39 Gilligans and 17 Kivlehan's.
There is one Kivlehan at Rosses Point Co. Sligo (see the townland mentioned in Griffith Valuation)
Most of the addresses can be tied with some work to the area's back in the 1840's and example would be Rosses Point. You can then write to them and see if you couldn't spur some interest. The Irish still in place seem to have less interest in their histories than immigrants. I think that one person/ address would be a good start. No postal codes are required the addresses are sufficient for mail delivery.