Any special distribution for nonprofits should include accessibility features and easily-findable documentation on them.
There are several Open Source screenreaders for linux text mode. The one I use is brltty, which gives braille output and some speech. There is also speakup, a voice output screen reader, YASR (Yet Another Screen Reader), also voice output, and emacspeak. For the GUI front, Gnopernicus, with both braille and speech output, is under active development for Gnome. It is part of the curent Gnome desktop release. KDE also has an accessibility effort.
There is also a debian-accessibility list, and subscribed to it.