ya in the cave just about the only cave you have use flash and south of eterna under the bike road. I searched every nook and crany and not a single one has showed up. all i've been getting out of there is zubat and geodude.
As I said, all it takes is time. Every time you encounter a pokemon there, you have a chance to find whatever you can there based on their meet percentage. Gible has a VERY low meet percentage and can take forever to find.