The easiest centralized exchange to get IQ on Ethereum is Binance. IQ is also available on Upbit and Crypto.com.
The DEX with the most liquidity for IQ on Ethereum and Polygon is Fraxswap with IQ-FRAX pairs on both ETH and Polygon. Sushiswap has an IQ-ETH pair and Quickswap has an IQ-MATIC pair. Zapper also allows for IQ swaps on ETH and Polygon.