Hmm, if that site has any way to download they sure want to hide it. If you haven't, I'd try making an account if it's free. Maybe they only give downloads out to members.
I couldn't find any dead animal models, most of which were for a price, but the most I was able to find were some skulls, if those would interest you at all:
http://archive3d.net/?tag=SkullA dead bird, I'm not familiar with this site so I'm not sure if they're free or not:
http://www.123dapp.com/Catch/Dead-Bird/1913638That's all I was able to really find. Hope this helps!