If you do a search with the terms sushi com chocolate (sushi with chocolate) you will find plenty of recepies. Nevertheless, it's certainly not a trend, I have ate sweet sushi before but I had never heard of norimaki with chocolate before.
It's really common to find sweet temakis ("sweet kones") for dessert, I wouldn't be surprised to find one with chocolate, but they certainly don't have fish on them :) They are not technically temaki in my opinion, as they are normally not rolled in nori.
It depends on where you are, but I'd search for temaki doce (sweet temaki), along with the name of the city where you are to find places to eat.
