I too need more Itso cubes, I have my LPs in 16 or so, and need another 9 cubes. Very hard to find, frustrating to not have them available.
I missed a batch of them on craigslist recently, they went too fast.
That said, Ikea is supposed to be bringing the Nornas sideboard to the US in February 2015. That might be a nicer solution, and very sturdy.