Joseph Jenkins, the original author of the Humanure Handbook makes it available in .pdf form for free on his website: http://humanurehandbook.com/
Understanding the principles behind how it works is key to using this method.
We've used sawdust toilets several times in the past, once during an extended power outage and a second, longer instance when our 20+ year old well silted in and we were without running water for about 10 days.
If someone needed to use this in an urban setting, they can purchase pine shavings from a pet or farm supply store.and mix a bit of cedar shavings to keep the odor down.
I didn't know The Humanure Handbook was free. That is great information! I've been handing it out to people who I think would benefit from it, but since it is openly available, I'll just send them the link from now on.