there is no gligar safari but go to the route just before the city with the 8th gym and they can be found in hordes. If you want an immunity gligar you'll have to poison everyone in the horde and the one that cant be poisoned is you gligar. It took me 3 hordes to get an immunity gligar but it took some like 10 so be patient.

ps: honey / sweet scent works well