Berries are only produced by female plants, so what you saw at your nursery were all females :-) If you grow them in your garden, you will need at least one male plant in order to fertilize the females for berry production. There's a fair number of male selections out there - ask at your local nursery or look at others (or order online or by mail). Because they are not as showy as the females, male plants don't tend to be quite as numerous in commerce.

The catalog I recieve from Forest Farm has a chart that shows males that bloom at the same time as each type of female commonly sold. I have used this chart with great success. I do not know if it shows up on forestfarm.net, but, if you knew the sort you purchased I would look on the chart to show the best male sort. I have wild ones less than half a mile from here, by the creek, but they did not pollinate mine. My first purchases were just labeled winterberry, which was not much help.

Yes, it is definitely important to know the name of the female clone in order to obtain a suitable male :-) The attached link may help to narrow down the right selection. FWIW, 'Jim Dandy' (aka 'Early Male') and 'Southern Gentleman' (aka 'Late Male') are perhaps the two most common male clones and one or the other should be appropriate for your gals. Or get one of each and it's pretty much guaranteed you'll get a good crop of berries.

Here is a link that might be useful: Ilex verticillata