blood from a stone/turnip, one can't get

This is a hopeless source of help (money, comfort, and so forth). Both stone and turnip date from the nineteenth century, and other versions exist in numerous languages. Dickens used the stone analogy a number of times, in David Copperfield, Our Mutual Friend, and other works, and health-food trends notwithstanding, it is more common today than turnip. However, Clive Cussler had the latter in Sahara (1992): “‘You can’t squeeze blood out of a turnip,’ said Giordino. ‘It’s a miracle we made it this far.’”