Statutory recording of marriages only started in 1845. Prior to that only the church maintained records, and even those were often incomplete. According to the PRONI guide to church records, Ballygawley Presbyterian’s records start in 1842. So prior to that they either weren’t keeping any, or the records are lost. There are no alternative sources in that situation.
Tradition was to marry in the bride’s church after which she’d attend her husband’s. So it’s possible that the marriage was in a different church but if it was in Ballygawley then there are no records to find.
Regarding burial places, Presbyterians generally didn’t keep burial records as you have evidently found. You haven’t said what Joseph’s occupation was. If a farm labourer then he probably couldn’t afford a gravestone and so would be buried in an unmarked grave. The vast majority of the population in the 1800s were in unmarked graves. If that is the case, then again if the family don’t know, then you may struggle to find it. If he was a farmer then a gravestone is more likely.
People weren’t always buried in the graveyards of the church they attended (there might have been a family plot elsewhere) and it’s common to find Presbyterians in Church of Ireland graveyards. But if there wasn’t a gravestone, you will struggle to find the place of burial. It wasn’t common in rural areas to put a notice in the papers and so that’s unlikely to help either.
