Given how old this thread is I'm guessing any advice is a little outdated, but here are a few suggestions:
Ribombee: A nice Fairy/Bug type which can be used to set up sticky webs. Also has a high special attack and speed stat which gives it quite a lot of stopping power.
Mega Scizor: Having a steel type is always nice to deal with fairy types, and technician buffed bullet punch can be super handy. Additionally, Scizor's typing helps with you deal with rock and flying types, though you must be careful with fire types.
Volcarona: A very solid option with good stats and access to quiver dance like Ribombee, unfortunately 4x weak to rock but still a great sweeper.
Araquanid: Another sticky web setter, but with Water Bubble Araquanid would be a great way to help you deal with fire types that get brought to the gym
Escavalier: Same useful typing as Scizor, with access to Knock Off and Close Combat
Heracross: A bulky fighting type to help you deal with rock types and hits hard with Guts. Unfortunately 4x weak to flying.
Galvantula/Vikavolt: Not the most competitive Pokemon but might be useful in dealing with flying types.
Honourable mentions: Golisopod, Scolopide and Yanmega.
It's worth noting that quite a few of the above can learn defog, which could prove quite useful considering the threat stealth rock poses to an all bug and often 4x weak team.