I was at L'Orient last year and didn't enjoy it - very big and commercial. But just about everywhere you will find "Fest Noz" at weekends, small festivals with everyone dancing in the park, very nice. Look for posters plus ask at tourist offices, & ask around generally. There are web sites about festivals in Brittany ... I might get back to you with URLs, or you can try your own search.
I seem to recall there used to be a festival in Quimper. Any one know of it?