I don't recall any service like that. It sounds good, assuming the market still have an interest on free trading calls. I doubt you can find out their private/paid calls since you'll have to spend a lot of money doing that.

Most traders that I know of follows Telegram channel regularly to check signals, some of them also use Discord. I personally only follow The Dude and Coin Bureau, not because they give trading calls, but because they shared lots of good info for free.