Essentially what observ said.

I've never gotten an EX from a gym with less than gold medal though. So the best course of action are:

1) Do raids on the EX gyms nearest to you especially weekend mornings.
2) Train your gym level for those gyms to gold. This will take a long time...
3) Add friends and send daily presents to the active folks in your area to level up friendship and leech pass..hahhaha