The definitive source is the London Gazette. That link takes you directly to the search page.
Put the dates you are interested in into the relevant boxes. (There are records after 1993 of MMs awarded before 1993, so put the end date as 2010.)
Now put the words 'military medal' in the "with the exact phrase" box
Put the words 'Northern Ireland' in the "with all the words" box.You will get loads of records, and will have to trawl through them all to find out which ones were awarded for service in NI.
If you are interested in a particular person, put their surname in the "with at least one of the words" box as well. (This will give you every page on which that surname and the words military medal occur, not just the ones where the MM was given to that surname.) You can do this with regiments, ranks or any other search term you want (service numbers are particularly good).