It seems the Arch Linux Template doesn't come with qubes-usb-proxy. I couldn't find it using pacman/yaourt neither. So I copied the files manually from the repository and it worked.
https://github.com/QubesOS/qubes-app-linux-usb-proxy
Is there a package for it somewhere? Should I make one and send a PR? I never did an Arch Linux package, but if some one could point me the direction I could try.
Best regards!