yep you can still grab it. Here’s the US store link:
https://store.apple.com/us/product/MC742ZM/A?fnode=MTY1NDA5OQ&mco=MTg2OTU0NzM
The official specs say it’s not compatible, but I assure you it is and works well. The installation instructions are slightly different but the card goes in pretty easily (make sure you place it in the bottom PCIe slot). The fiddliest part was getting included power adapter attached to the logic board (tight spaces). if you have two monitors, make sure you order the mini-display > DVI adapter as this card only has one DVI port (+2 mini-display ports).
Don’t do what I did and put the standard nVidia card (mine was the 7300GT) into the machine at the same time as it seriously bottlenecks FCPX and I couldn’t even edit plain old DV without having it set to proxy playback mode, and even then transitions/very simple titles wouldn’t playback real-time un-rendered. With the 7300GT removed, my machine absolutely flew when I was playing around with some 1080p media last night.
All the best!