What kind of music is this and where can I find more?
It’s choral music. You can find more of it Roman Catholic churches or in high schools across the country.
For a more modern take on the same concept, allow me to suggest some Polyphonic Spree. You’ll prolly recognize this song, but it’s safe to say you prolly haven’t heard this version before.
Second that. If you liked the video you posted, I would suggest looking at some Palestrina, or even Thomas Tallis (the one from the 16th century).