There was definitely one at the very end . . . but other than that, you're right. I suppose because the Navi had kicked out all the avatars and only let Grace back in after Jake pleaded with them to do so, there just wasn't a need for them. Also after Jake was accepted as one of the Navi, Grace focused all her attention on him and after Quidditch tried to intervene she moved to the remote base in the Hallelujah mountains. Without her around all the other avatars were likely just restricted to that area around the bunk house. I assume more of them would have fought in the final battle if they could have but only the ones that were able to escape in the chopper were able to i.e. Jake and Norm.

I think you can see them again at the very end of the movie when their kicking the humans off the planet, I believe some of them were wearing human clothes so I always assumed those were Avatars and not Navi.