Correct link should be: http://www.hwjyw.com/textbooks/downloads/zhongwen/
This is posted in Japanese category though so might not be relevant for the original poster.
Fililng in missing words (“cloze testing”) is definitely a good idea, and could probably be done automatically by Skritter as it already knows which characters you are likely to get wrong in a sentence. I suspect we’ll need to wait a while for it though.