i got all these chocolate molds you are talking about(all sea molds,etc)from a little bakery not too far from me. she has all kinds. anything you want to make.lol i have purchased chocolate molds on line from , i think, candyland crafts dot com. try looking that up. they have lots of molds too.
I just did a beach themed cake last week and used chocolate molds for the shells. I did some solid white and I also put a couple of pieces of light cocoa chips and swirled it for a more realistic look. There's a pic in my album.