I really want to add a Camerupt in my black 2 team without trading. Is there any chance for getting a Numel/Camerupt in hidden grottoes?
Unfortunately, it does not appear to be possible. In order to get Numel/Camperupt in Black 2, a trade is required. Neither Numel (and Camperupt) or its version exclusive counterpart (Spoink/Grumpig) can be found in Hidden Grottos, as well. This also applies to the Dream World, where Spoink is exclusive to Black 2 and Numel is exlcusive to White 2.
I Hope I Helped, and I'm sorry for the lack of Camerupt in Black 2.
Unfortunately, there is not. It's impossible to find Numel or Camerupt in a Hidden Grotto.
Hope I helped!