What is that quest that you need Thievs Guild armor? are PC player? you can always use cheats to get some.
There's a point in the TG questline where you get upgraded armor but you must trade in the TG stuff you already have in order for that to happen. If you no longer have it, you don't have anything to trade in for the upgraded stuff and the quest stalls out.
OP: supposedly there is TG armor, boots, etc. that is placed around the cistern and adjoining areas that you can take for free once you're a member. Have you tried looking around to see if anything is there? If so take them and see if Tonilia will accept them as a trade-in for your upgraded gear.