I don't think it is possible for the OP to buy that Ikea product, as their cage is too wide. (Unless I read that wrong.) Unfortunately, I don't know where else to buy one of those, but if there is only a little amount of overhang on each side of the storage unit, it should be ok for you to get the Ikea one.
To make it work with wider cage, you'll need 4 of those, and a sheet of plywood. You'll have to position the 4 units to support the wood at each corner of the cage, then bolt the wood onto the top of the shelves.