In reply to Just Tintin:
Basically, off the ferry you can turn left towards Ploumanach, or right to Kerlouan. The bouldering on the Kerlouan side is better, and drolex has given you the best lead for info, but basically it's miles and miles of very open beach with thousands of granite boulders. Quality is a but variable, but you can just rock up anywhere and get a decent session in - they have a big bouldering festival here at the end of some summers (last time we were there was 2012 and they were getting ready). Mats useful, and if the weather's at all windy, just get on the autoroute and head south - it's no place to be on a grey day.
On the Ploumanach side, it's a lot more sheltered and there's more infrastructure in terms of shopping and food. The area around Tregastel has some stuff but again, just drifting around gives plenty to go at.
We generally stop off on the way down and up most years, but have never bothered with a topo.
Martin