I've listed below all the Anglesey parish baptisms I can find (from FindmyPast) with father Elias Jones and mother Mary, between 1795 and 1815 - I expect you have already looked at them.
3 Feb 1798, Llanfechell - John son of Elias Jones, Cefngwyn & Mary his wife
28 Nov 1799, Llanfairynghornwy - William Elias son of Elias Jones of the parish of Llanfechell & Mary Roberts his wife
5 Jul 1801, Cerrigceinwen - Catherine dau. of Elias Jones of Ty Rhedyn by Mary his wife
13 Feb 1803, Cerrigceinwen - Richard son of Elias Jones of Ty Rhedyn by Mary his wife
3 Mar 1805, Cerrigceinwen - Ellin dau. of Elias Jones of Trehwfa by Mary his wife
23 Nov 1806, Cerrigceinwen - Jane dau. of Elias Jones of Trehwfa fawr by Mary his wife
6 May 1810, Cerrigceinwen - Thomas son of Elias Jones & Mary his wife
There are grounds for thinking this is a single family.
There is a younger son, Owen, who had a non-conformist baptism at Horeb C.M. Chapel, Llangristiolus on 21 Mar 1814. He was born in Cerrigceinwen parish and is described as the son of Elias Jones, farmer of Trehwfa (parish of birth - Cerrigceinwen) and Mary Roberts (parish of birth - Llanfechell).
Like you I can't find a marriage for Elias and Mary. Unfortunately Llanfechell marriages 1790-1800 do not appear on FindmyPast.
It is possible some of the children of Elias and Mary were known by patronymic names, so surname Elias rather than Jones, in later records.
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