Discovered my first Space Ponies! as well during the Beta on an occupied world.

Ditto

I found it twice in two different games in the exact same planet (relatively, map was slightly different).

So wait...they're something you find on a random planet then?

Well I suppose you were playing Loyalist then ^^.

It's (nearly) impossible to get the planet/achievement when playing rebel, as you will usually research the ally with neutral factions. This makes you unable to attack the planet, so you can't get it. Quite frustrating.