various ways to do that theres one peer to peer exchange called hodlhodl that i personally use or else you can use localbitcoins but for that you must need KYC now so i suggest you buy a couple of identities from darknet first and then KYC wont be an issue for you, Some people also sell verified localbitcoins accounts , theres also remitano exchange which is good for peer to peer btc and usdt trades but in all cases to stay truly anonymous you would need to meet the sellers and pay hand to hand cash