I was wanting to download the free DLC that is available for Coin Rush, and I can't find the stupid shop button. Does the shop unlock after you complete a certain number of coin rush games or something? I got the game from the eShop.

This is driving me crazy. Is there some sort of game update that need to be installed maybe?

I may have answered my own question.

Switched up my Google search terms and found this:

"To access the New Super Mario Bros. 2 Shop, it must first be activated by a SpotPass notification. This will cause a Shop button to appear on the title screen. Notifications may not arrive immediately if it's been awhile since you last played."

WHY WOULD THEY DO THAT!

The reason it wasn't working for me is that I hadn't relaunched the game since getting the SpotPass notification.

You also have to have passed the first world to open up the coin rush mode.