Mushroom Patches and Mushroom Circles of all kinds. The increase doesn't apply to other things that may drop Glimmerdust, like Old Logs, Weeds, and the Magic Garden.
Now there is a solution being made, perhaps someone should merge all the glimmerdust threads - there are quite a few!!!
A push for the Glimmer Dust drop rates is now live. You should get them more often from all mushroom patches/circles. We also adjusted some gem costs on all blocks, beams, glues, pastes, and feasts. They were significantly cheaper then their material costs, and so they were raised to be a bit more in line with our intentions. They're still cheaper then their individual parts, just a little less now.