From Dave Maynard, with thanks:
Some gateposts I’ve noticed in the area north of Whitland. Just a small sample, plenty of other big stones off the Preselis, these are just a few I’ve noticed. I think I'll do a bicycle mounted survey when the weather is better, but before the vegetation grows too much.
The issue of mauls at the supposed quarries appears to have been avoided. To get any stone out of the parent rock will result in lots of flakes and spalls. The only other option is if they had previously been detached.