when you buy a domain most part of the hosts will offer you free coupons, just check for the best deals
you can get them from hosting companies .. Most of sellers now used to buy a hosting acc , get the vouchers then ask for a refund !! it is not a Good Way
As far as I know, facebook ad coupons only useable for the first time advertiser. Once facebook user use a facebook ads coupon or discount, they cannot use different new coupons for their campaign. In this forum, on voucher section, you can find many members selling facebook ads coupon view bucks per one facebook coupon worth tens to hundreds dollars.