I play the Mars "Exclusion Zone" mission on lvl 22. Use the consumable the gives you bonus glimmer for Cabal and run through the first encounter. There's a bunch of Cabal majors and they drop a lot of the items you can turn in to the Cryptarch for 200 glimmer each plus the consumable gives you nice glimmer. Just make sure to leave one of the phalanx alive at the end or the Centurion so you can die and reset the checkpoint.