You should grind Zweilous off of Audino on route 23, or whichever route is right before victory road, they give a good chunk of exp. Also use rare candies if you have them?
Blue Shard Locations:
Route 13, Route 13, Route 17, Route 17 (With Dowsing Machine), Desert Resort, Desert Resort (With Dowsing Machine), Mistralton Cave, Village Bridge, Relic Passage (With Dowsing Machine), PWT (Lose at PWT), Clay Tunnel (With Dowsing Machine), Reversal Mountain (With Dowsing Machine), Seaside Cave (With Dowsing Machine)
You can also get them in Join Avenue apparently. Good luck!