Did you try quilt shops? Many gave it.
Also, if you are going to buy it online, many places sell it, including JoAnns.
http://www.joann.com/joann/catalog/p...RODID=prd56691
Connecting threads and Amazon are options too.
If you go to Joanns, they do sell some dye fixatives in the dyeing section, but not the Retayne brand name.
Hope this helps.