Dynamite Comics has a 12 card set inserted in its comics which has Red Sonja meeting the Mars Attacks aliens.

It is a 4 issue series which came out monthly between April and July. All 12 comics with the cards have been released.

Each of the 4 issues has 3 different covers bagged with the trading cards. Thankfully the cards are not random. To get all 12 cards, you must buy all 12 covers.