I think you can find those promotions on their ANN thread. Try to visit the Service Announcements board or Exchanges. Last time I remember, most of them give you a bonus but you can only use it as a trading fee discount. Bittrex is the last one to do it iirc. Not to mention most of the time they ask you for extensive KYC.

Don't be hopeful about this, you probably get better 'results' from gambling deposit promos than an exchange deposit bonus.