I got mine at the post office too.  There is a factory that makes cardboard boxes and supplies bubble wrap, tape etc. but I did not actually go as the factory is in industrial area (too far for me).  If you need a lot then it might be worth it - I don't have the number but I found it online.

On the other hand you can have a moving company actually pack your stuff without moving it - I think the cost was reasonable but I prefer to do my own packing :)