Drops from Skadi the Ruthless in Utgarde Pinnacle on heroic mode. It has an extremely low (1% - 2%) drop chance. It also has a chance to be listed on the Black Market Auction House.
Here you can buy Blue Proto-Drake for EU or US Servers.
You'll get guide for getting Blue Proto-Drake
You'll be able to get Blue Proto-Drake 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