Dragons think of their hoards primarily as wealth, rather than tools. According to the Draconomicon, when calculating the values of their hoards, dragons consider magic items to be worth the half of their listed prices that they can be conveniently sold for. The upshot of this is that dragons will tend not to buy nor sell magic items. They'll keep and if possible use whatever magic items they acquire, of course. And they do have three times the standard number of random magic items for monsters of their respective CRs.
What constitutes a "full array"?