I have death certs and burial records in Llanferres Parish Registers for:
Catherine Parry, Pentre, Llanferres, died 28 October 1847, aged 58, burial 02 Nov 1847
John Parry , of Tafarn Gelyn, Llanferres, died 31 March 1853, aged 66, burial 04 April 1853
Family Search showed this entry on Billion Graves as a possible match
https://billiongraves.com/grave/John-Parry/25806314 Though the extreme right of the stone isn't included on the photo and its difficult to make out, I believe it is likely to be for the people I am looking for.
Its billed as being in Llanrhydd Cemetery, but Google maps shows that location (shown on the page) as being at or very near to St Berre's church in Llanferres and Llanrhydd Cemetery appears to be about 4 or 5 miles away.
I did see that the NA have, in RG67, reference to gravestones/graves that were removed from Llanferres (doesn't give any details as to where to) and the date range includes these years of death, but the records are listed as being in the database on deceased online. I checked the deceased online site for the specific database and these people do not turn up in the search :-(
Though I appear to have found a likely gravestone photo, I am still uncertain about where the stone is located - Llanferres or Llanrhydd and not sure how or where to find out.
Boo