The hawkstrider drops from Kael'thas Sunstrider in Magisters' Terrace on heroic mode. It can also be found listed on the Black Market Auction House.
Here you can buy Swift White Hawkstrider for EU or US Servers.
You'll get guide for getting Swift White Hawkstrider
You'll be able to get Swift White Hawkstrider
Swift White Hawkstrider mount
Additional budget for Character transfer or Character boost to max level. BMAH Services in Shadowlands now requirement to have a max level character on server, so Trial character will not work.
Free time on evening, if you choose selfplay option