I don't know where else to ask. I am lvl 79 and have the Legendary Gardener badge. However, the wizard is not offered any prequest for the Avalon gardener. Interesting enough, this wiz reached lvl 15 gardener prior to doing any quest in Avalon and now he is nearly finished with Avalon.
Yes, I have already back tracked and double checked every NPC up to where I am. I know who gives the prequest in Caliburn. It's just not offered.
UPDATE:
I am now lvl 80 and almost complete with Avalon. I believe when back tracking the quest line for eventually spawning Roger the Shrubber, I can not tell where Gwendolyn is located in Dun Dura. I have completed all prequest to that point so far as I remember. I wish I knew what the issue is.....
After you get to Dun Dura and talk to Gwendolyn, you can't miss her, you will get a quest from one of the NPCs in Caliburn...something about a shrubbery, during those side quests you find Roger in Dun Dura and then eventually (when those quests are done) he moves to Abbey Rd where you can access him as the gardening trainer.
The real problem is that people post, without having any knowledge on the matter.
To the OP, send in a bug report, you have done everything correctly, except that KI for some reason, figured you would have all that done, before you got to be level 12 gardener. So, if you passed level 12 gardener and then got to the requirements of that quest, you will miss being able to get the quest.
I too am a level 15 gardener and I also did not get the quest. It is a bug for those people out there, that think they know better, so quit making excuses and let KI fix this bug.