A gentleman called Dan Norris has blogged about his failed startup (Inform.ly) extensively, as well as published a Kindle book called "The 7-Day Startup" which talks about this and the lessons that he learnt extensively. I'd recommend you to google him and check out his book, as you're spot on that the net is full of success stories but not many are brave enough to discuss their failures.
I would go looking at public records of failed companies. One way to get really detailed information would be to call the former owners of these defunct companies or their underings and possibly even pay them for there analysis of what happened and what they would do differently. You could contact angel investors and all other investment groups like them, which usually have more failures than successes so they might be a good source and tell them that you would be willing to share your finding with them to help them know who and what to stay away from. Call me if you want more thought on this, thanks...Ken Queen
I do disagree, Infact failures are easy to find and they are strewn across the corporate world. Since You are writing case study these links below will be helpful for you:
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath