there are standing stones (meini hirion) all around that church, but I never knew about the font.
at crickhowell is the growing stone (in TMA), at the next village north is Druid's Altar (marked on OS maps).
north of the village is a wood with 2 stones (marked on OS maps).
Then very little of anything until you get up near the source of the river, up in the Black Mountains. Whereupon you'll find the maenhir Maen Llwyd.
the good bit is that the font is in a village called Llanbedr, that is inbetween Maen Llwyd and the Druid's Altar.
Made my day, cheers baza.