I was looking at all the potion options and I noticed some pets that I'm pretty sure can't be created the normal way, like the Yaherra or Neela. So are these just older pets I will probably never have, or is there a different way to acquire them? (Like buying a specific object).

At the Zapper you can zap your pet into a random species/color, including experiments, or if you scroll to the bottom create or transform your pet into a Qrykee or Yaherra.

Blobland is where you can get a blob.

Neelas are bought from the cash shop, but you can buy the potions from other players through user shops.

Zentus come from the Zentu bath

The only tricky one is Bhakoru, which you can get by buying the nostalgic instructions, completing the quest, and transforming one of you pets using the toy and an Essence of Melody, then using a color potion on it to change it to the color you want.

thanks so much!