I would suggest shipping 6" plants with no pot, and only a little bit of soil mix surrounding the roots. Clip the leaves (haircut) a day or two prior to shipping, then hydrate well. Wrap them completely, together with a wet paper towel around all the roots, in plastic wrap. You can create a separate, labeled bundle for each variety. Mail in a box immediately. The transplants will survive about 1 week like that, if it's no too hot. Hopefully it doesn't take that long.
On receipt, the plant stalks will likely be curved significantly. You just plant them with the root system pointing down, regardless of the way the stalk is pointing. Tough love. The stalks will figure out which way to grow.
Bob