There are about 30 Mannion's in the telephone book for Sligo. Match up your place names with addresses, for instance a Mannion in Collooney. There are 13 Johnston's out of the 151 the phone books suggests. (For some reason the phone book will include any one whose first or last name begins with J) Also 25 McDermott's and 15 Lynch, addresses given are sufficient for mail delivery.
One of the Mannion's is named Dermott Mannion, there is a Padraig (Peter?)
Outline what you know in a letter, photocopy and mail to a few in the pertinent areas. You can do this while you wait to be contacted through the message board. Stamps are
You can find births, marriages and deaths after 1864
on the website www.familysearch.org
(up to 1950's)
There is also a website that Co. Sligo belongs to a History Foundation with Parish records if you need one.
I have a CD set from the Latter DAy Saints - no longer available with births from 1864-1875 and also
Church of Ireland marriages 1845-1862. If anyone fits I can look them up.