I sold off my thieves guild armor long before getting to the point in the quest line where it is apparently "required" to have at least 1 piece of it to progress and have Tonila upgrade the armor, use her as a fence or finish the Under New Management quest. I checked the vendor I sold the armor to and it is no longer on him. Every time I talk to Tonila she goes thru that dialog about having to have at least 1 piece....gives you the option to say I dont have it anymore...but then she says I better find at least 1 piece but it seems impossible to get it back.
Wasnt sure if this is a quest bug or where those are posted to.
T.