You could use the digits of some transcendental number, say, pi. Skip zeros, then each digit yields two moves. For the first move, lows(1,2,3) gives stone, mids(4,5,6) gives paper, and highs(7,8,9) gives scissors. For the second move use mod 3, so 0 gives stone, 1 gives paper, and 2 gives scissors.
> Humans are really bad at random
You could use the digits of some transcendental number, say, pi. Skip zeros, then each digit yields two moves. For the first move, lows(1,2,3) gives stone, mids(4,5,6) gives paper, and highs(7,8,9) gives scissors. For the second move use mod 3, so 0 gives stone, 1 gives paper, and 2 gives scissors.