In the old PSN Store, its had a ''All DLC'', then you had to choose ''A-L'', ''M-R'' & ''S-Z'' and then simply choose a game and you will see all it's DLC.
Now, this is no longer here but there too many things making searching way too complicated for nothing. ''Character, Level, Stage, ect.'', all those categories just make thing complicated.
Now I am trying to find all the dlc of Dead or Alive 5 and Street Fighter X Tekken but I can't because I only see the latest one. Searching doesn't help because its lead me to buying the game, not the DLCs.
Right now, browing the PSN Store is just not enjoyable.
While I realize it is a crappy work around, I would suggest you go here:
This will show you all the DLC available. Then you can know/find exactly what you want and just type the item title into your search to the PSN Store to go right to it.