The beach at RAF Valley is about the only place. I know of. Get an ordnance Survey map. They'll all be listed on it. It's not the biggest of islands is it??
When I first moved up here 20 years ago I was told there was one green lane on Angelesy. I've never found it, bit it's probably been downgraded by now.
There are a couple of little bits around but not anything worth travelling far for. BTW driving on the dunes and/or beach at Cymyran (rear of RAF Valley) is illegal loads of people have been dobbed in by the local residents and the RAF blokes.