Did you search on www.3dcafe.com ?
EDIT - uh, just checked it, no success. There are plenty mermaids you can buy, eg. from turbosquid. If I was you, I'd take any woman mesh and remove the legs and add a mermaid fish tail (since you already got the fishes), this should be easy when you have basic skills and a tool.
EDIT - uh, just checked it, no success. There are plenty mermaids you can buy, eg. from turbosquid. If I was you, I'd take any woman mesh and remove the legs and add a mermaid fish tail (since you already got the fishes), this should be easy when you have basic skills and a tool.