These MIDI files all come from the Classial Music Archives (www.classicalarchives.com). I have collected them using a "free login" that lets you download 5 files per day. You can collect files yourself, but you will have to wend your way through the procedure for establishing your login. I recommend you do that when you have the time, because there are thousands of classical music files available, and they can be used to produce sheet music, as well as serving as a superb medium for practicing and rehearsing, or even providing accompaniement for a solo performance.
To use a MIDI file in the ways mentioned above you will need a MIDI player. Good ones (Finale, Sebelius, Cakewalk) can cost a lot of money, but there are also a variety of free players available for download on the Internet (see below for a good free player). However, if you click on one of the files here (or its copy that you have downloaded to your computer) your media player will play it for you.
The following is a free copy of Sweet MIDI Player from Roni Music, in Sweden. This MIDI player is for Windows, and you must download it and run it (a .exe program) to install the Sweet MIDI Player on your PC. To download, right click with your PC mouse on the preceding link. This free version will not allow you to change or store a MIDI file, but it does allow "solo" and "mute" and "volume" control on each track, and most important "tempo change" specified as + or - percent. Try -40% on the Sanctus for initial learning. Your vocal part usually has "Choir Aahs" as its instrument designation. Tracks 11-16 are used for the 6 vocal parts of the Sanctus.
If you have an Apple computer, you need to go directly to the Roni Music website to download the correct version for your particular model of Apple.