Commander, that one near Bala looks nice, I hadn't realised they split the camping from the caravanning. It can be difficult to find good campsites near pubs in Wales, the nicer, quiter sites tend to be in farmer's fields in the middle of nowehere, like Cae Du that always get recommendations here (3 miles from Tywyn but fantastic views). You could also try Cae Adda in Trawsfynydd (has a pub in village). But if you are looking to book for this weekend, you might struggle with those. If so, try searching ukcampsite.
EDIT: And if you want quiet, and you are looking for this weekend or any time in the summer holidays, avoid Snowdonia and Bala! Around Llyn Vyrynwy or Clywedog or the Elan valley is just a beautiful.