Certified GKH Gardening Expert
If you can't find them at your local big box stores, I would recommend going to some of your local smaller nurseries (such as Valley Garden Center or Waugh's Nursery Center). They should carry them or be able to tell you who in the area does. It may also be a matter of timing. Most places do not carry the same selection of plants year round. They will carry what is popular at that time of year. It is easiest to find wisteria when wisteria is in bloom, because it is on people's minds. If you can't find it locally yet, wait until it blooms in your area and check the stores again.
If all else fails, there are many reputable online sellers who will ship to your home.