Here are some simple first step that will at the very least fix any of the underlying issues that were addressed by Google.
1. Contact the past SEO Company directly, explain to them the warnings from Google and see if they will give you that info. You never know as it never hurts to try. Many SEO companies would like to keep there reputation even after being dismissed by a client.
2.What If that doesn't work? Contact the site owners per each site and explain to them that you have been hired to address SEO warning by Google caused by a prior seo company and you would like to resolve it by requesting them to delete the articles. This is actually a win/win because I don't know any website owner that really wants garbage on there site.
3. I don't see why there would not be an opportunity to increase there rankings again. I would be upfront with them and explain to them that its pretty much like starting from scratch and that past rankings are irreverent. Send them the release about the JCPENNY incident so they can familiarize themselves with the situation that they have encountered. http://www.pcmag.com/article2/0,2817,2380306,00.asp
4. Once you've solved these issues, do what you do best and optimize there off-page SEO, since you said there on-page is pretty good.
You said they want results yesterday. Don't give in to there pressure by making any false promises. Just be straight forward. It's better to lose a client with a piece of mind then make them false promises that will end up haunting you later.
