Here in
Canada, and also in the
USA, one can send any quantity of materials for the
blind, be it
literature in
braille, or text-reading devices, or (I believe)
medical supplies.
When I worked at Canada Post in the wintertime, there was quite a lot of stuff sent from doctors to indivduals under the heading "materials for the blind". So, the lesson in this is to blind everyone to whom you intend to send mail, to be sure to write to them in braille to avoid fraudulent activity, and to acquire those handy little stickers that replace the stamp.
Another trick could be to work at Canada Post in the wintertime, and to drop mail in the delivery bins directly, but this is very risky. It is even illegal when working there to pick out mail destined to you if you should come across it.
Other ways (that I have just brainstormed) to use the Postal Service for free:
This last is free, but it is free for them.