The tusks drop from Garrosh after the final battle of the Siege of Orgrimmar. They are epic-quality DPS plate shoulders. It also can be listed on the Black Market Auction House.
Here you can buy Tusks of Mannoroth for EU or US Servers.
Also you'll get guide for receiving Tusks of Mannoroth
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