You can use this public endpoint which is a read-only list of all Grant Names & Ethereum Addresses:
https://gitcoin.co/grants/grants.json
Also check out these docs on the smart contract architecture of Gitcoin Grants: https://github.com/gitcoinco/web/blob/master/docs/GRANTS.md
and the Gitcoin Grants API:
https://github.com/gitcoinco/web/blob/master/docs/API.md