According to their Twitter yes, 5 stones are guaranteed the day of the event from trainer battles. I don't think AI battles are included here, but we'll see how it pans out for Europe to know for sure. If they do more stone-based community days I'd bet they would make at least 5 available again so everyone gets multiple chances at evolving one.
An aside, that's some bum luck. My most recent stones have come from a loss and training. A training session against Blanche actually gave me a stone and a rare candy.