In a low-magic, radioactive desert world, my players are probably about to fight a trio of henchmen loyal to the local despotic ruler. These henchmen are the loyal enforcers of the ruling party and have been working together for many years. Even though they often carry out missions alone, I thought it'd be fun to give them a unified tactic, given that they're very familiar with one another's fighting styles. I've gone with poison.

It centers around a gnome rogue, who uses the Poisoner archetype. He uses alchemy to craft the blood of mutants into poison (a contact poison), which he then converts into injury and inhaled variants. So in battle, he's going to be using poisoned daggers and throwing capsules of poison gas around to debilitate his foes.

My question: what options exist to help his party members avoid being poisoned themselves? Antitoxin is helpful but expensive (in this world, anyway), and of course there's the Great Fortitude feat, but I'm hoping for something more specific. I told my players that they could use anything from PF or 3.5, including third party (though nobody took me up on that) so that's the parameters I'm after. The whole trio is a rogue, a fighter, and a Skirmisher ranger, so no divine help, and no magic items are available either. Ideally I would like a feat like Great Fortitude, but focused on poison for a better bonus.