I just read this thread. Quickertek does still make the ucard 4 upgrade for the 2012 Mac Mini, and pretty much any MacBook made between 2008-2012. As of today in January 2020 the company asks $149 for the card. Here's the current link. If the product page goes dead over time, do what I just did, and check their site menu product page…
https://www.quickertek.com/product/ucard-4/
I bought a Late 2012 Mac Mini Server today. I'm excited!