Okay now.
I am going to explain how to get Ad-Hoc Party.
First you need a jap PSN account.
If you enter the PS Store choose the lowest button on the left side.
Then you choose the Japanese sign for A which is あ then again あ.
Now the Store displays all DLC with an A.
Ad-Hoc Party has a green sign and the name アドホツク... - it is visible without scrolling down
EDIT: It has a Video file with the same pic next to it, the only difference is on the bottom of the Videopic there is written Video and the name of the Video is in []