Yeah I read about that attachment point thing. I haven't tried it myself as it requires downloading three specific pieces of software, but may at some point. Too many other things to do though.
Usually the only time I think you'll ever get a custom model out of someone is if you announce your project and collect a team for it. I know a bunch of the other warcraft map sites have places for this, but you'll need to have a really strong vision and be able to convince people to join the cause (good luck).
The other way would to be to do the tides of blood and work backwards. After your map gains some notoriety, you may attract the attention of some modellers/skinners who will do the model for you. Don't get carried away though. These days it seems tob is more about looking better than it plays.
Another option would be to find a model that is in the general shape of what you're looking for and reskin it (with the author's permit). There's some goblin models on the war3search that could perhaps be reskinned into that annoying little runt.