Hey! Welcome aboard, muppetmad!
First of all, I'm not entirely certain if there was ever an Animal backpack made. If so, I've never heard of it.
If you're really interested in an Animal backpack, though, you might be able to make one yourself. They sell large plush Animal dolls online. You could take one of them and turn it into a backpack. That way, you could also use his arms/legs as shoulder straps. Make it look like he's holding on to you.
Sorry I couldn't be more help!
Oh, and, please. While we all like to pick on each other here (sometimes we go overboard), this is a friendly forum, and many of us would like it to remain so.