M.2 SSD's are still in transition which makes things a bit dicey here.
As you weren't clear on which system you have I've listed both:
Here's a workable enclosure for your 2012 MacBook Air: OWC Envoy Portable, Bus-Powered USB 3.0 SSD Enclosure.
Here's the enclosure for your 2013 MacBook Air: OWC Envoy Pro Portable, Bus-Powered USB 3.0 Enclosure For Apple Flash SSDs (June 2013-Current Mac Models)
As to the M.2 Blade SSD I would stick with what the major 3rd parties offer. I would recommend you contact Transcend directly to see what they have. It's possible they don't have anything currently. Part of the problem here is the manufactures are buying most of what is being made so its hard to get the newer models of SSD blade drives.
I should point out from our experience many of the ones sold on eBay are not worth the risk. We tried getting a few and out of the five we bought only one worked and we got burnt on two as the seller wouldn't give us our money back (not a good story).