The 7th Gym use a 2vs2 battle, Solarock and Lunatone. Both are Rock/Psychic with the Levitate characteristic.
If your having real difficulty you could try Sharpedo and Cacturne. Both are Dark so resist Psychic atatcks. Plus Grass and Water are both super effective against rock. Cacturne could use Leech Seed and Drop Root so it stays in the game longer.