Sadly you won't find an external case or SATA adapter for your SSD. Apple uses a proprietary SSD.
Your only option here is to find a friend that has the same series as your system and is willing for you to swap out his SSD for yours. Then you can copy off the data onto a USB flash drive or setup your friends system on a network so you can then use the Apple migration assistant to clone your SSD's data onto your new system.
Presently that is how we do it when we have to recover a users system.
Well time heals all wounds!
OWC now has a full line up of external cases to hold both the Air, Retina & iMac systems which host M.2 SSD's. Follow this link: OWC Envoy Pro Portable, Bus-Powered USB 3.0 Enclosure For Apple Flash SSDs (June 2013-Current Mac Models)