If you figured out how to ask a question on this site then surely you can google the question. It's explained on dozens of sites.
Even this one!
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Don't be a wanker, by the time it took u to write that reply u could've just said PVP.
So yea, best way to get is PVP and there is a small chance of getting through research.
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There is no guaranteed way to get a Sinnoh Stone.
The weekly Field Research breakthroughs have a chance to contain a Sinnoh Stone. Trainer battles also have a chance to give a Sinnoh Stone (up to once per day against team leaders and up to thrice per day against other players).
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PVP, research, and patience. Throughout many battles, and weeks of grinding research tasks, I still haven't received one after they were no longer guaranteed. But I can wait, it's not like there's a deadline.
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I'm swimming in them - nearly all from battles. Make sure you get all your four battles in every day and RNG will soon favour you.
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Don’t worry about it.... if it’s are too lazy to google it or look it up on this site.... you are probably going to lazy to be grinding stones
