Re: how to get promotional code link
Promo codes offer varies from country to country. Additionally there are other terms and conditions also which have to be adhered before applying the promo code.
Here's the country specific policy for Promo Code: https://support.google.com/adwordspolicy/answer/1396257?hl=en
In case, you are looking for India specific offer, here's the link to review: https://www.google.co.in/adwords/coupons/?sourceid=awo&subid=in-en-et-fbxr