I think your friend might be Scrappy Pangoro.
With Scrappy, Pangoro can hit Sandygast with False Swipe. It also has strong Dark-type moves to KO unwanted Sandygast. Seeing as Scrappy is Pangoro's Hidden Ability, you will want to chain for a Scrappy Pancham outside of Po Town, using Skill Swap or Entrainment to see which ones are Scrappy.
Once you have a Pangoro, and have given it a swell nickname (for example, Jack Black Eye), chain for Sandygast as you would normally: using False Swipe, then KOing Sandygast with Crunch/Night Slash while occasionally False Swiping a new Sandygast to prevent the chain from breaking. Be sure to pack lots of Hyper Potions and Leppa Berries, as well as Adrenaline Orbs and a Pokémon with Stun Spore for when you've found your Shiny Sandygast.