The point of these proprietary institutional key systems is that you can't. The blank is patented, and the authorized manufacturer will only sell it to authorized representatives of an institution which has a contract to use that key system. It will further guarantee that only one institution gets to use that system per geographical region.
It's "security through the inordinate difficulty of acquiring an object with a particular shape." Cheap 3D printing of metal might put an end to that strategy.
There is an image processing script, that will take a picture of the key and deduce the key number, or bitting code, or "key cut code", which is an expression of the heights for each pin. [1] [2]
Then you can plug that bitting code into a script which will generate an STL model for the key. [3]
I did this, except I measured the key with calibers and back-calculated the key number. I printed the key on a cheap Prusa I3 in ABS, it was not impressive in terms of resolution or strength, but it did work in my house. I carefully tested it because I thought it might break off in the lock, and it felt weak, but worked -- definitely good enough for a single covert access, or even use as an emergency backup key to hide somewhere.
No fancy metal printer needed, and you could write a script to pull pictures of keys out of twitter or whatever and automate the process.
i'd start by plugging "key blank" into your favorite search engine. if that fails you horribly, you can buy brass all over the internet: http://www.onlinemetals.com/https://www.metalsdepot.com/ mcmaster-carr, or amazon. i suggest a pair of calipers, too.
