You can indeed buy an adapter;
here is a link to one for your model.
Apple was still using SATA for flash in 2011, so you have a bunch of great value options. Look up MyDigitalSSD. They have 250 and 500GB SATA sticks that fit this adapter for $75 and $130, respectively. I put their 250 in my 2010 Air; speeds are fine and TRIM works if you use 'trimforce'.
If you care more about performance, probably go for like a Samsung 850 EVO. Roughly $100 for 250 and $180 for 500 on the street.
Heck, go for Transcend's own SATA M.2 blades (MTS800 series), which are about the same prices as the Samsung ones. And consider for a moment how crazy that is, given that the components (the flash chips and the controller chip) on the Transcend MTS800 blades are *EXACTLY THE SAME* as the ones they use on their JetDrives (the Transcend blades that fit in a MacBook without an adapter). So you save nearly $100 on the storage itself by using a $10-15 adapter. The mark-up on the JetDrives and OWC Auras is nuts...
-- Nathan
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