You can buy these in Smith's, but try working it out first!
Both cubes must have the numerals 1 and 2 on a face, to cater for 11 and 22. Both must also have 0 on a face if dates before the 10th are to be represented with both cubes. The numerals 3 to 8 then each need to appear once on any face. All 12 faces have now been used. The only way to include 9 is to realise that it is simply 6 upside down!