I don't stop by here often, but I just happened to see this post after trying to hunt down the same tubs. Those IRIS tubs have been discontinued. The tubs that come with the CSerpents rack are also IRIS, but they are the line that is manufactured for The Container Store.
I tested the fit since I own both of these racks. The CSerpents tubs are smaller that the RBI. In fact, they are small enough to actually nest inside the RBI tubs. The GOOD news is that they are exactly the same height, so you can use them without having to worry about escape.
My RBI rack is in good condition but half the tubs got crushed when I moved. Luckily you can use the other tubs in a pinch.