You can purchase API3 from these places
Go to Kucoin.com
The People's Exchange
Go to Uniswap
Uniswap is a secure platform that makes it easy to buy, sell, and store cryptocurrency like Bitcoin, Ethereum, Stellar Lumens and more.
Go to Poloniex
Welcome to Poloniex. We are a US-based digital asset exchange offering maximum security and advanced trading features.
Go to OkEx