>>52813732It's easier to despawn them by running away. Here's where I got my shiny Sandy Shocks. If you do the Electric sandwich, the only things that spawn near the rubble area are Raichu and Sandy Shocks.
Don't go down the slope, just run around the dark dip in the rubble. If the shiny isn't there, run up to this rock to despawn all of the Sandy Shocks and repeat.