Is there a Thieves' Guild in Valoran?

If the Elder Scrolls series has shown me anything, it's that thievery can be rather lucrative. Some of our resident Champions have been thieves in the past ( to name a few), but never stuck with it as a lasting occupation, or rather don't give off the vibe of "thief".

Additionally, when thievery gets organized under a guild in a fantasy setting, lots of good stories can result from it. Oblivion and Skyrim set good examples.

Now, this is my opinion, but I think a sort of "Thieves' Guild" in LoL's setting would fit in perfectly. An organization with no allegiance to any city-state or nation, whose job is to relieve the rich and wealthy of their valuables. I can't think of a reason why not to have it.