I think Flewellin is essentially a Welsh name. English families arrived on the Castlecomer plateau in at least two ways - firstly with the Wandesfordes, but also after the uprising of 1798 families were uprooted from Wexford - many of these families went on to emigrate on mass to Canada.
Wexford has very close links with Wales, which is essentially a country built on coal mining.
Interestingly though there are Flewellin records on ancestry going back to the 1600s in Yorkshire.
Kirklington (original home of the Wandesfords) records can also be trawled on ancestry - going back to the 1500s and beyond.