Out of curiousity I did a quck check, and sodium perborate IS avalable as a granular solid. One source that lists it is a company I've bought from before The Chemistry Store http://www.thechemistrystore.com in FL. I'm going to try making some from the hydrogen peroxide formula, and if I find it's something I like will probably buy a 5lb pail from them, as I believe it was something like $8.00 or so for what would be a long time supply.

I'm curious, would changing the strength of the dilution from 1% to 2% or even 3% change the amount of speed increase in the film?