You actually can get all of the Zodiacs by breeding them together, or Zodiac x Diamond. Using the hidden colour, ie Zodiac x Virtue can give you the Zodiac in question, but will cut out on any of them without pink as a hidden colour as a fail, plus you get a ton of other fails added into the mix!
Breeding them is frustrating due to way black splits, so it just takes a lot of patience
So Zodiac x Zodiac can = all Zodiac dragons, plus pure colours such as magic, night, water etc (best option if you're only interested in Zodiac)
And Zodiac x Diamond can = all Zodiac dragons, pure colours, diamond hybrids such as gold (got mine this way) plus other mixed fails
While Zodiac x Virtue can = Aries, Scorpio, and 30+ others including long fails such as sunrises, lucks and corals, and some good fails such as Mask
I have five Zodiacs, Leo of course, Aquarius and Capricorn (Leo x Leo), and Pisces, Scorpio (Leo x Aquarius)