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.
That is a better alternative if you cant find any exchange that give bonus then you can find many other gambling sites that have this.
Only few exchange doing that promotion and mostly only new exchange have that.