Fully Proportional 3x3x6 and 3x3x7

[Colin]

I have a 3x3xn collection that includes 1 through 5. I would like to extend it to include 6 and 7, but the only ones I can find are not proportional. Does anyone know where I can purchase one or how I can mod a more common puzzle to create one? I have seen 3x3x7s before that are fully proportional (and functional), such as superantoniovivaldi's. However, I have never seen a 6.