Hard drive upgrades for the 2014 13 inch retina Macook Pro

Nobody makes PCIe SSD upgrades for the Haswell Macs.

Apple uses a proprietary, non-M.2 PCIe blade form.

My guess is that if other manufacturers like OWC started making those proprietary form factor PCIe SSDs, Apple threatened to sue them.

 

There is a thread or two on this very subject on the first page at the moment.

Nobody makes them, and nobody likelly will. The only way to get one is getting a used one off of ebay.