I checked Bulbapedia, and it said "most dungeons", which isn't really detailed at all. Unfortunately, I do not personally know what dungeons you can find them in. However, you can buy them at the Kecleon Shop (if they're in stock) for 800 Poke. However, there's a better method (in my opinion): the Recycle Shop. You can trade two Escape Orbs for a Reviver Seed. I don't remember when Reviver Seeds are unlocked in the Recycle Shop, but I have them unlocked and I haven't even got to the point you're at yet! But you may be wondering how to get Escape Orbs easily. Don't fret, there's a way. A very easy one: Marowak's Dojo! Go into any one of the training mazes, and you can find Oran Berries, and, more importantly, Escape Orbs! They're pretty common, so you wont be going into a maze a hundred times just to find one. They're also a nice way to train up your team! So when you have some Escape Orbs (and, hopefully, leveled up), trade them in for Reviver Seeds at the Recycle Shop, and then you can storm into the dungeon! I recommend doing this until you have plenty of them.
Hope I helped!