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There are two trios of glowflies that spawn on the road near Setting Sun Garrison (seen @ 9:30am server), close together with a fairly quick respawn. I had seen the glowflies as backup with other pets in the Vale, but didn't see them spawning themselves until I had unlocked the Garrison quests in the Vale for Golden Lotus.
EDIT: There are also 2-3 groups of these that spawn in Kun-Lai, right outside the gates to the Vale.
I caught a level 24 this morning on the road near Setting Sun Garrison at around 9:30am server. They appear to share spawns with the Effervescent Glowflies there, which spawn in groups of three. I was hunting for a rare glowfly and one of the glowfly trios was replaced by moths on the third re-spawn. Phasing linked to Golden Lotus progression may or may not play a part - I didn't see any battle pets in this region of the Vale until the Garrison opened up to me, but might have just been a fluke.