I finally more or less got to a point where I can open the my concrete shop. It is organized by Concrete and Patterned Concrete. It is also separated by Base Color (Azure, Berry, Blue, etc.) and then sorted by sub color (Ashen, Cold, Dark, etc.). I currently have every color of concrete and patterned. Some is in limited quantities, but I am restocking it constantly.
You can get to it via:
TNT Mall Wall > Illuminati Concrete
GTG Hub > Illuminati Concrete
TNT Sovereign Wall > Cthulhu I > Concrete