By looking on
www.familysearch.com. Then click on Search the Ancestors.
I did find a Samuel Samuel who married an Elizabeth David in Llanelly on 12
April 1822.
By then putting Samuel Samuel and Elizabeth in the parents and refining to
Wales several children born to a Samuel and Elizabeth turn up. Includes a
David. Only problem family search tend to put all children born to a Samuel
and Elizabeth Samuel down so it is a question of sorting out if they belong
to your line. Hopefully this may be a lead.
Pam