Just before Agate Circus, decided i want to bring a Sheer Force nidoking along with me beforehand but forgot he needs a Moon Stone lol. i've sold the one in the Slums and backtracked to Byxbision Wasteland as there was apparently one hidden in a rock after the first sliding steel beam coming from the 'hidden tunnel' - alas i could not locate it. Tried my hand at mining for the past 3 hours as well and yet to find one