DeFi (Decentralized Finance) are not companies and more like community projects. You can purchase a specific crypto token associated with a particular DeFi project using a DeX (Decentralized Exchange) which is in itself a DeFi project You can find a list of of DeFi projects here: https://defipulse.com/ There are also DeFi projects on the Binance Smartchain but if you're in the US, don't bother unless you can handle VPN and confident you won't make a mistake https://www.defistation.io/ You'll need to make sure you can interact with smart contracts using compatible wallets. The L1 smart contract platforms are technically Defi, Eth, Sol, Xtz, Bnb, Dot, and even oracles, Link You can do research on Coinmarketcap and Coingecko websites and the specific project's website