Just drops randomly by liking Cabal. I have like 325 of them. I haven't used them since Year 1 and they nerfed farming that first Mars mission, which was the way to earn some hummer back in the day (without a VoG Gatekeeper checkpoint).

That was a better farm for glimmer prior to rise of iron. The items that you activate to get glimmer from killing enemies are mostly irrelevant now because a ghost shell with perks for dropping glimmer similarly activate the exact same thing permanently with no time limit and they don't stack. People have hundreds because they've been playing for 2+ years and haven't had a use for them since year 1. The only source is them dropping off of cabal yellow bars so the best place to get them is from the exclusion zone on hard difficulty farm spot. Now, you'd be better off with a ghost for fallen and going to spend some time in the archons forge. The combination of the glimmer from killing fallen, the house banners dropping for 200 each and dismantling all of the blue engrams should get you more than enough glimmer and you might actually get some useful drops form there outside of that. The dread explorer shell from the quest in the Taken king (asks you to do the outbound signal mission) isperfevt for RoI. It's a perfect intillect discipline roll with spinmetal and fallen perks. Otherwise you can check the vendors around the tower inventories or farm one out in the archons forge. What do you need mass amounts of glimmer for anyway? There really isn't any major reason to spend a lot of time farming it. If you're buying heavy synth and have some ether seeds, go see variks in the reef. He sells them for 250 and an ether seed as opposed to the usual 950. You're better off getting heavy synth from Xur for strange coins though.

Exclusion zone on harder difficulty don't kill everything and wipe and repeat. This was used and abused years ago when I needed glimmer lol

Cabal majors drop them

Kill Cabal bosses