Yesterday, I finally got the perfect Jellicent - Cursed Body with Modest nature.
With a little help from one of my Elgyems of course thanks to Synchronize.
Yes, I have lots of Elgyems that I use to search for particular natures.
A good tip I recommend for those who play Black or White, catch some Elgyems in Celestial Tower or Munnas in the Dreamyard and use the ones with Synchronize. Catch lots of them with Quick Balls and you'll end up with a variety of natures eventually. Then take the one with the nature you're searching for and you'll get that 50% chance of running into a Pokemon with the same nature.