Glim can be easily obtained by fishing. Common and uncommon fish can deconstruct for 3-100 Glim each, with rares granting 1,000.
Glim can be dropped by grass in all Biomes, and by defeating enemies. The easiest and fastest way to farm for it is to go to a low level adventure zone and destroy the grass and enemies you find there. The Fae Trickster's Glitter Bombs are good for this. The Knight's or the Dracolyte's basic attacks are excellent choices as well, and the Neon Ninja's superb speed makes it highly recommended. It's tedious, and takes a lot of time. If you can, find a friend or group and stick together so you'll all get drops from everything being destroyed.
Mounts trample grasses, allowing players to ride through instead.