Check with your local nursery to see what they have available. Back to top I planted over 20 holly bushes along the property line of my house a couple of years ago. They have grown nicely, but are still small plants. I am hoping they will give me privacy in the coming years. In all probability, they are simply not old enough to start producing berries.
Hollies have separate female and male plants, and only the females can have berries.
With that many plants, surely you have some males and female bushes in the bunch, so that they can produce berries. If the plants have started blooming, you can dissect a bloom to check for male or female parts. A male will have several stamens in the center of the flower, a female will have a sole pistil. I think you should simply give them time to mature and begin producing berries. We have a two year old yaupon holly tree on our patio.