If you want to plant a specific variety of hydrangea, you would be better off mail ordering it. Alternatively, you could contact your local nursery and ask them if they could order one for you. You're likely never to come across "Phantom" hydrangea just by looking around.

I hate to be the bearer of bad news, but those are only viable to zone 8. You're in zone 9b. There are some heat-tolerant hydrangeas that can be grown in your zone, but this isn't one of them, in fact, oakleaf hydrangeas do not get enough cold south of 9a. That being said, if you have a large evergreen tree, like a live oak, to put one under, I hear Nikko Blue does well down there. I never tried one when I was there, so I can't speak from experience. I'm sure others who have had success will chime in. I do know they need afternoon shade.

Zones are very important here. There are a lot of northern plants that just won't do well in our hot, humid climate, hydrangeas being one of them. Ask me, I know. I have serious ZDD and moved up here because I could not grow a lot of my favorite plants in 9b/10a.

ETA: I don't agree that you should mail order plants, because in my experience, many mail-order catalogs do not differentiate between 9a and 9b, and it can make the difference between a plant thriving or not.

Too bad about Phantom. Yes, hydrangea paniculata need more cold than we have here. Hydrangea macrophylla do acceptably well in the St. Pete/Tampa area. I can recommend Endless Summer and Bloomstruck.

I forgot they weren't right for this zone. Luis told me that and to plant macs instead last spring on the Hydrangea forum when I asked if they could even be grown here. I had Nikko and ES in zone 8.

When should I begin to look for them in the stores? I think I bought Nikko bare root from Sam's Club in our previous state. We have a Costco membership here, dj they show up there also?

The best time to find them in the big box nurseries is April-May. They reliably get them in for Mother's Day. You might find them anytime though. This is probably the least likely time of year to find them because they like to concentrate on Mums and soon Poinsettias for Christmas.