I am in Arena 2, have 592 trophies, and I have had no luck finding the Mini P.E.K.K.A., even though I've opened a number of chests. What should I do to get Mini P.E.K.K.A.? I am trying to collect all commons and rares available for my arena.
Just keep playing, you will get it eventually.
There is no short-cut to getting a mini pekka, or any other troop, directly.
You will get the mini pekka after a while of playing. Just be patient.
But if you really want a mini pekka, you can improve your odds of getting it, by buying chests like the giant chest, magical chest or super magical chest from in-game with real money.
Cards you have not yet unlocked can be bought in the card shop, so pop in everyday to check if the mini pekka is amongst one of the available cards to buy!
Because the mini pekka is a rare, the best odds of getting one will be by buying a super magical chest, because it is stated in-game that the super magical chest contains at least 115 rares (and 19 epics), thus you have a very high chance of getting a mini pekka in that chest.