I'm not really too keen on how this whole process works but I recently got pokemon black 2 and I noticed that Tentacool isn't in either versions.

so is there a way to get myself one of those?

Do I have to trade with someone for something?

If so, what?

I figured there are peeps out there that just have random pokes just laying around made from software onto DSs.

I'd just like a specially defensive, HP one.

and if it's not too much to ask, Shiny would be nice.