Beyond Prax and Dragon Pass, Glorantha's been described more in fan publications than official Chaosium products. Not Canon, AIUI, but quite a lot of it written by people like MOB, Nick Brooke, Jeff Richard, Sandy Petersen, and Greg Stafford. The best current example would be A Rough Guide to Glamour (the Lunar Empire's capital city).
If you're willing to go back to RQ 3 and hunt among the 'zines, yes, there's wild and wonderful material on places far from Dragon Pass. Tradetalk used to devote every second issue to some odd corner of the Gloranthan Lozenge. Back in the 90s, Tales of t