Hard to make recipes as this process is is very loose in variables intrinsically. Different teas or coffee beans may have darker brews even from the same brand. But it's easy to mess around and test.
You just really have to experiment with temps and soak times, and concentrations of tea and coffee. As well as focusing on how you print as staining darkens it overall since it affects the base of the paper but not the blacks as true toners would.
Another thing, your stained prints smell really good after as a bonus when they are dried. Haha