Last time I saw an active portal to Show Room, it was through Coils R Us, but those portals have been up and down, and the place didn’t seem to be actively maintained anymore.
Places I personally check for forged goods:
The Golden Fist, which has a portal at TNT
EZPZ, which has a TNT portal, as well as a mall spot at DK mall (though stock has been a little light recently)
Fantasy Tree, which has good high-tier stuff