I didn't see an entry for them in the Subetapedia? They're a full species with basic colors though so they can't be lab pets? And only the neela is in the cash shop.

I'd really like to get a sweetheart one! But I was hoping to create one instead of buying an elixir?

You can get one from the Pet Zapper for 500,000 sP.

To create one from scratch, you have to do so at the zapper.

https://subeta.net/explore/zapper.php

They are a full species with various colors now, but they started out as an experiment pet. They got changed to a full species after a community vote/donation thing on a few experiments that people wanted to see become full pets.

So it IS a lab pet!

The Subetapedia articles are released when the corresponding Lifelike dolls are released. That is the only thing this means. This also means some pets do not have an entry and will not have one for years.