What pets can't be adopted and are only available through potions? Just curious !

I know Neela is one ^.^

You can create a common Neela in the Cash Shop on the same page you buy the potions.

Cadogres + Endeavors are only available to be created during Masquerade, I believe.

There aren't any pets that can only be created through potions :)

Bhakoru aren't available to be adopted or created in the normal sense. If you want one you will probably need another user to create or morph one of your existing pets, assuming you may not have been here for the Blake Steele plot where they became accessible to users.

there is also the bumbus, which is only obtainable through the blue building.

Swampies and Darkonites can only be obtained from Elixirs or the Zapper afaik.