Does anybody know where I can find a list of previous champion sales?

I want to make something similar to the free week rotation chart someone made lately, so we can have an idea what champs are likely to go on sale. I have found an old thread on the forums, but that is outdated, and the "sales" category in the news section of the site only goes for the past 10 sales. Does anybody know of a good way to find all of these?