Answer: The hollies are dioecious, meaning you need male and female plants to produce berries. These particular named hollies are the berry producing female form, so you need to add a male that blooms at the same time to serve as a pollen source.
Ebony Magic is grouped within the Blue or Meserve Hollies (hybrids of I. rugosa and I. aquifolium) so you could use Blue Stallion, a widely available male selection that blooms over a relatively long period, as the pollen source. You could also probably use a male selection of English Holly (I. aquifolium).
Most nurseries will sell the appropriate male for the females they offer. The male should be planted within about a hundred feet or so of the females, at a ratio of about one male to five or six females. Often enough, there are male plants on neighboring properties sufficient to avoid purchasing one of your own, but perhaps this is not the case in your location.
Keep in mind also that weather conditions such as excessive rain during the blooming period may inhibit pollination by insects in the spring, and that ill-timed pruning can remove either the flower buds in spring or the immature fruit during the growing season.
I hope this helps you trouble shoot.
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