You can purchase DYDX from these places
Go to Binance
To provide users with more secure and convenient block-chain asset exchange services, polymerization of global high-quality block chain assets, is committed to creating a world-class block chain asset trading platform.
Go to Poloniex
Welcome to Poloniex. We are a US-based digital asset exchange offering maximum security and advanced trading features.
Go to Bitstamp
Bitstamp is run from the United Kingdom and is one of the most popular fiat to Bitcoin exchanges.
Go to HitBTC
The most advanced cryptocurrency exchange to buy and sell Bitcoin, Ethereum, Litecoin, Monero, ZCash, DigitalNote, Ardor.
Go to Kraken
Buy, sell and margin trade Bitcoin (BTC) and Etherum (ETH) in exchange with EUR, USD, CAD, GBP, and JPY.
Go to Paribu