Hi Ellen,
I would love to see what I can do to help you find out more about the cemetery where Thomas O'Shay was buried.
Before 1864 records were kept in the form of church and parish records, and while some of these have regrettably been lost over the years, all the surviving records have been sorted into county based
genealogical centres. Since your ancestors lived in Dublin around that time, you can get in touch with the
Archives in Dublin for more information. They might have some documents on where Thomas was buried.
I hope this was helpful, and hopefully you'll be able to get some more input via the Community! :)
Melin