You'll need the HM Whirlpool and teach it to one of your Pokemon and you can pass the Whirlpools blocking Whirlpool Cave.
get a Pokemon with a ressisstance
nerd
yes they could
Simply use the HM Cut.
on the right there is a 2nd path
YES THERE ARE WHIRLPOOLS IN New Zealand
You Can't
You get him in trade with a friend or you do the event that past already.
you have got to trade him from a past game
That depends. Which path are you talking about?
yes trade with a friend
must obtain the required number of league badges