Statutory death records for Northern Ireland from 1922 onwards are not on-line anywhere. You need to contact GRONI, in Belfast if you want a copy of his death cert. They cost £15.http://www.nidirect.gov.uk/gro
To find Patrick’s marriage, you really need his wife’s name. Otherwise you are just guessing. So you need to get a birth certificate for one of his children. Anne Jane was born in Leitrim. What looks to be her birth was registered in Carrick on Shannon Apr – Jun 1885 Volume 3, page 76. Order a copy of that from GRO Roscommon or from GRONI..
The townland that your ancestor lived in was Drumbinnion. The modern Longhill Road runs across it. It’s a few miles south of Dromore, off the A 32.