Most garden stores sell it. If they don't just ask and they could get it for you. We always had it in the spring and early summer. It is such an easy plant to grow and will surely take over so it is best in a pot. You can also grow it indoors. I hope you find some. MB
I have catnip herb, catnip toys, and catnip hydrosol (a catnip spray I distill in my copper still, made from fresh catnip leaves) in my store - http://www.prairielandherbs.com/pets.htm