The Reins of the Vitreous Stone Drake drops from Slabhide in the Stonecore on both Normal and Heroic modes. It also has a chance to be listed on the Black Market Auction House.
Here you can buy Vitreous Stone Drake for EU or US Servers.
You'll get guide for getting Vitreous Stone Drake
You'll be able to get Vitreous Stone Drake
Vitreous Stone 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