PRONI in Belfast holds microfilm copies of the original Glendermott CoI church registers.
https://www.nidirect.gov.uk/proniAvailable in the PRONI search room:
Church of Ireland, Glendermott (Derry diocese)
Baptisms, 1810-1900; marriages, 1808-1900; burials, 1828-94.
PRONI reference: MIC1/108
The records are not on-line anywhere as far as is known. The PRONI copy is on microfilm, so you either need to visit yourself, or instruct a researcher to go on your behalf.
KG