I use it too.  I picked up a 30 lb bag at the last show from one of the
shelter.  However if you contact Zupreem by e-mail they will send you
retailer that handle it (both local and Internet).  Just go to their
web-site and click on contact us.  Our local Petsmart carries it, but
it's expensive.
 
On-line Ferret Depot seems to have the best deals.
 
Hope this helps
 
Joy and her foursome.
[Posted in FML issue 4878]