You can purchase MITHRIL from these places
Go to Bitfinex
The largest and most advanced cryptocurrencies exchange
Go to Bithumb
Bithumb is one of the largest exchanges in South Korea, allowing users to buy/sell/store Bitcoin and Ethereum.
Go to HitBTC
The most advanced cryptocurrency exchange to buy and sell Bitcoin, Ethereum, Litecoin, Monero, ZCash, DigitalNote, Ardor.
Go to OkEx