Yeah, I know it sucks. This happens when a game studio no longer holds the rights to a certain franchise..they then have to remove the DLC from the marketplace. It happened with the Ubisoft Naruto game too.
I missed out when they made it available for that one week so I was never able to buy it...but they made it so you could still complete the game's achievement list without owning the DLC pack.
All you have to do is download the compatibility pack from the market place, find someone who has purchased the DLC a while back and is willing to help you out.
Join their game and complete all of the new simulator missions and you will be able to unlock the last few points.
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