I had a comment today on how to find sea-glass beach. This is how we were shown to find it. I started from Blackbeards in Isabel. The X is where we were told Seaglass beach is.
This is a little closer picture of it. You can walk all the way down to the beach from Isabel. You walk through a narrow street between some houses, and the road leads all the way down to the beach. You can see the old shipwreck off to your right when you hit the beach: