I went looking for what in the world is "Affresh" since I'd never heard of it. Turns out it's just oxygen bleach. So, Seventh Generation dishwasher powder or Oxy-Clean bleach should do the same thing.

I was wondering whether crystalline citric acid might be an alternative for cleaning the washer (although as I said, in 11 years it's never seemed to need it, other than popping out the detergent tray for a good rinse and scrub once in a while).