I recently purchased a miniature of the Undead Leviathan from Warploque Miniatures. The figure is not currently in their online catalog, but if you send them an e-mail, it seems that they are more than happy to cast one up for you.
There is a pirate ship wreck that can be mounted on the whale's back, but I opted not to buy it since I was only interested in the whale.
The model comes in 5 pieces, and is cast in a light gray resin. The fit of the pieces is excellent, and I did not find it necessary to do any clean-up on the model at all.
The Warploque undead whale is very reminiscent of Keith Thompson's cover art for the Expeditious Retreat Press module
A Magical Society—Aggressive Ecology: The Undead Leviathan, though each is its own beast.
Scaling out to just over 40' in length at 1/72, I felt that the resin model was somewhat undersized for a leviathan, so I wanted to make it a bit longer.
I cut out a section from a whale skeleton that was used as a promotional toy from Burger King, and grafted it onto the Undead Leviathan.
I had to carve the vertebrae to make them better defined and match with those of the resin model, but it took less than 10 minutes to do so.
Kneadatite, plastic sprue, and J-B Weld was used to add gobbets of decaying flesh onto the bones.
The additional length messes up the whale's proportions, but that is the price for having a whale that is 50' long as opposed to 40' long.