WARC has case studies, as does AdAge.com.  

For AdAge.com, just do a keyword search on the phrase "case study" and you'll find them.

For WARC, you're better off using their case study search tool.

The best starting place for best practice content is WARC.  

It offers two main types of Best Practice articles:

–   "How to ...".  These are generally the longer pieces.
–   "What we know about ...".  These are short, concise and concrete pieces.

Because navigating in WARC is sometimes a bit complicated, here's a link to all their content on the broad subject category "Non-profit, public sector & education".