My maxed out Mid-2012 13 inch MBP - 16GB of ram and 1.2TB of SSD! : r/mac
Amazon.com: MCE Technologies 500GB Internal SSD Flash Upgrade for 13" and 15" MacBook Pro with Retina Display (Mid 2012 - Early 2013) - Includes Installation Kit! : Electronics
How to make your MacBook Pro faster – upgrading a MacBook Pro mid-2012 to SSD and more RAM memory - Andy the webdeveloper
OWC SSD Kits For MacBook Pro Retina Display 2012 - 2013
New 2.5" SSD won't fit - my MacBook pro says it's a mid 2012 15" model - Ask Different
Amazon.com: MCE Technologies 250GB Internal Flash SSD Upgrade for MacBook Pro Retina (Mid 2012 - Early 2013) - Includes USB 3.0 Enclosure for Original Drive & Install Kit! : Electronics
Macbook Pro Retina 2012 Wi-Fi Upgrade - A Leslie Wong Blog