mermaid, trumpet or fishtail style with a sash
try looking at ruffledblog, they specialize in showcasing vintage style weddings.
http://ruffledblog.com/
I think you will like this dress from this featured wedding, all it needs is a sash, but you can buy sashes separately. Tthis is what she says about it, "My dress is a Cymbeline dress. I had it altered into a mermaid fit by having the torso extended and tucked and had part of the train cut off and sewn to make the dress a one shoulder.":
http://ruffledblog.com/jenn-brads-indie-wedding/
there are some handmade and vintage ones on etsy:
http://www.etsy.com/search_results.php?search_query=merma...