Christine:
Civil registation of deaths started in 1864. Prior to that date some churches retained death info but Oughteragh parish did not.
The 1857 Griffiths Valuation head of household listing for Oughteragh civil parish shows a Patrick King in Curraghnabania townland. Don't know if this record is for your Patrick or not. If he died lets say 1850, the record would be for a different Patrick but if he died around 1857, it could be his record.
The townland could be Curraghnabania, civil parish Oughteragh Co. Leitrim.
I looked for Doonan records in the Griffiths and there were 14 Doonan households but none in Oughteragh parish so it would be difficult to figure where Bridget came from. The marriage normally occurred in the bride's parish so maybe her father had a very small holding and was not listed in the Griffiths.
Questions?
Roger