Yeah, Chimechos are incredibly rare, but I just get a pokemon with Thief or something (Mightyena works well here), and thief 'Spell Tag's (hold item that boosts Ghost-type attacks) from the Shuppets, then trade them to other real-world people in exchange for other items that I need.
Works well, as there are not easy to come by, and it kills time.
If you do this in conjunction with having a Zigzagoon/Linoone/or Phanphy in your team (pickup ability), and another pokemon with EXP Share on it, then you don't really waste your time that much at all, and it can be quite rewarding in the end when you do get your Chimecho/Duskull. (just remember to stop using Thief on those pokemon, they're weak to Dark attacks. I recommend having the Mightyena with OdourSleuth and Thief, and have another pokemon (like Zangoose / Nincada) with False Swipe. (OdourSleuth will make it so Ghost pokemon (like Shuppet) are no longer immune to Normal and Fighting type attacks).
Give it a shot!