TNZ nursery has a few listed. Here is a link that might be useful: TNZ Nursery

Yaupon is borderline in upper zone 7. Some cold years it can freeze back. I do not believe it is native to Long Island, but I could be wrong. Goodness, for zone 7 there are SO very many hollies that are better looking than American Holly. Fosters #2 is nice, fast, good berries. Smaller leafed. Nellie Stevens is the default holly planted here. Takes shearing very well, but does get TALL. Look into 'Mary Nell'. Incredible leaf gloss and BERRIES, oh so many berries most years. 'Blue Maid' is a nice very hardy blue holly which grows slowly to 12 feet. It takes its time and will not need much pruning. Castle Wall is a very upright grower. (another Blue Holly). Chindo Viburnum might be worth looking into, if it's hardy in your area. Fast grower, very glossy, no spines. This post was edited by dave_in_nova on Mon, Sep 16, 13 at 9:43

Here are some pictures of my bigger Hollies from March of last year. I think opinions were split between Ilex cornuta but leaning towards Nellie Stevens. Sam said"Your female holly is blooming now and has green stems, it has no I. opaca blood in it. Try searching your state's botanical garden website and compare to Nellie Stevens. NS is self-fruiting, did your tree bloom last year, did it make fruit? If not you may have one of several cornuta hybrids."

Very Cool!!! Wavecrest Nursery in Fennville, MI sells a number of I. opaca cultivars. Just this past summer, I purchased one called 'Dan Fenton' and am attempting it at my mother's in Coleman, Michigan. I know Dow Gardens in Midland has a cultivar which is doing quite well too.