You can purchase ARCBLOCK from these places
Go to IDEX
IDEX is the only Ethereum decentralized exchange with real-time trading and high transaction throughput.
Go to Bittrex
Bittrex is one of the larger crypto to crypto exchanges offering a large number of trading pairs into bitcoin - including all the major cryptos such as darkcoin, nextcoin and litecoin
Go to Bithumb
Bithumb is one of the largest exchanges in South Korea, allowing users to buy/sell/store Bitcoin and Ethereum.
Go to OkEx