you can use advanced forum search to "search threads" in "games" forums for keywords in "titles and first posts only" containing the beginning of the store's url (as it's likely to be linked in the op), ordered by date (ordering by date is important if you expect more than ~1000 results).
that will return a list of threads where either the game's or the author's entry in that store is linked in the op. keep in mind it doesn't mean the game was necessarily leaked from there (many games are available from more than one place).