There are numerous listings for it on Ebay. I haven't checked Amazon, but maybe there also. I am going to get from Ebay when I am ready. It's really hard to locate out there.
You can also go on etsy.com and look up duckweed or aquaponics and there is a person on there that sells it.
trickers pond supply ships it (out of ohio)
i've seen it on aquabid as well
Thanks everyone. Never thought of eBay or Etsy. I had some arrive today, but half of it was dead. They are sending a replacement, so we'll see how that goes, but I want to have a back up just in case.
most any pond store has it michael in seattle