Visited the area this summer noticed a site close to the beach Glan-Y-Mor, looked basic and when I got home checked reviews, seems to be a possible second best option to wild camping. Didnt stay so cannot recommend but would have a look if I was to be down that way in the future. TBH wasnt over impressed with the holiday/caravan sites in most of the surrounding area. We stayed at another small site near the entrance to the beach, (as it was empty the cassette time). Glan Morfar Mawr which was fine, very neat, almost too neat if you know what I mean.
If you are there suggest a small walk up the hill to a small chapel and graveyard, Sant Mihangel Treflys, superb 360 degree views. Cannot recommend any of the pubs, bus into Porthmadoc if you want a pint but I would check as I was told the contractor for the route had gone bust and it may be summer only anyway.