The designer stated on these boards that the publisher decided to include the mini-expansion in all copies, but they didn't get a chance to include the rules - hence the PDF on this site for the Utopian/Prestige planets.
We bought our copy on Amazon (USA) in early December (I unwrapped it on Christmas) - and I do not have any Prestige or Utopian planets.
Is there any way to buy or obtain the mini-expansion?
To the best of my knowledge, these were included in the first 5000 copies. My shrink-wrapped copy had a sticker on it letting me know that the bonus cards were included. It sounds like Amazon sent you one from the 5000-10000 batch.
Originally, three of those cards were exclusive to Kickstarters but was later changed to include both the Presteige and Utopian planets.