One of the places you can get three sets of the same tiles is on the Classic challenge for September 9th 2016 (change the date on your PC)
Straight away you can see 6 of the same type of tiles, just click them all away.
From the comments:
thomaskorat - I just got this on the Hard puzzle "X marks the spot". Don't need change the date!
tedebearvdh - I just got this on easy challenge for today (24/05/2017)