How do you get a rocky helmet in Pokemon Black and White?

You can't get a Rocky Helmet in Pokemon Black and White. The Rocky Helmet was introduced in Pokemon Black 2 and White 2.

If you're playing Black and White, there are other items that can help you with defense, like:

* Leftovers: Heals the holder a little every turn.

* Black Sludge: Heals the Poison-type holder a little every turn.

* White Herb: Cancels the effects of a stat-lowering move.

These items can be found in various places throughout the game, including shops, trainers, and hidden locations.