How that i find my promotions codes

[galacticarm]

If you mean the code you receive as a reward for selling/buying then:

New flash promo

Check your email for one titled: Your purchase of X qualifies for the Rebate Promo, redeem your Credits now! The instructions would say: Congrats, your purchase of X qualifies for the Rebate Promo. Simply open the notification for Rebate Promo (Menu > Notifications) to redeem your Y in Credits! These Credits will expire in 7 days so make sure to redeem and use them before then. You can check your Credit balance and expiration any time by visiting Menu > Balance. Have you redeemed it?

If you mean coupon/discount codes then check https://twitter.com/Gameflip when they post the codes.