Hi and welcome to the forum 
This should report what pamac did with your nvidia drivers:
$ cat /var/log/pacman.log |grep nvidia | tail -20
(last 20 lines of the pamac log mentioning nvidia)
I use 2 of the mirrors you have and they work perfectly for me so bit stumped what could cause this. does sudo pacman -Syu sync your database again and solve the download problem?
How do you check that the nvidia driver is not installed?
Could you provide an inxi please? and what does mhwd report ?
see: How to provide good information
edit: thak you for using the correct formatting, that makes it readable and searchable