The main thing is, just be patient and keep your eyes open. Punctata isn't a particularly rare Aerangis in cultivation, and they pop up on various vendors' sites and places like ebay throughout the year. Or least they have been showing up sporadically that way for the past few years since I started getting into Angraecoids a bit.
You will probably have to order online or consider a pretty significant drive if you plan to travel to a nursery that carries A. punctata. If you're ordering online, this really isn't the best time of year due to the cold weather. So if you decide you can't be patient, go ahead and pay extra for quicker shipping methods, heat packs, and insurance.
I didn't do an extensive search, but I see that
Tropical Orchid Farm has this species for sale currently. Other good places to keep your eyes on would be
Andy's,
Botanica Ltd and
Louisiana Orchid Connection.