Can you only get these guys from the pet agency or zapper?

I think at the moment that is the only way to get one as there is no elixir. You can probably also get one from the Loyalty Box since I think they let you choose a pet species.

The loyalty totem is only for choosing a pet color, not a species. But you should be able to also get one from the if you really wanted to go that route

I'm sure you've noticed the news, but urubu elixirs have just been released which are available at the Apocalyptic Apothecary. :D

I JUST SAW IT <3 ________