Note: There's still some confusion regarding Red Shards being obtainable from Antique Shop in Join Avenue. Red Shards' Bulbapedia page mentions they're obtainable from there, but Join Avenue's page doesn't list Red Shards as an item in the Antique Shop section.
A similar thing happened with Mistralton Cave being mentioned as a place to obtain them, but its page didn't mention Red Shards as an item. I edited that mistake on Red Shard's Bulbapedia page, but I'm not sure about the Join Avenue thing cause I've never played Black 2 or White 2.
Tl;dr: can someone confirm if Red Shards are obtainable from Antique Shop in Join Avenue or not?