Etherscan is a great place to find the source of the smart contract.

To find the address I have to the stateofthedapp website and the bottom of the website has a link to the etherscan. And in the contract tab, I was able to find the smart contract code there.

For an example here is the address to smartcontract for compound defi:

0x4ddc2d193948926d02f9b1fe9e1daa0718270ed5