It has from the start been offered by its inventor as a download for 3D printing (see the "About" section of the official site); it is also commercially manufactured, and available from Amazon. (See link from official site; if you don't live in North America, follow the link and then change the ".com" to the suffix for your regional Amazon.)
There is also an "X2-Cube" (3x7x7 with a 2x2x3 column omitted from each corner) and a planned "X-Cube 2" (2x4x4 with omitted corner columns).
MechanismEditThe X-Cube is essentially a shape mod of the 3x3x3. The X2-Cube has more freedom of movement, but not much more due to internal bandaging; it handles somewhat like a Professor Cube.