[ download virtual box ]
https://www.virtualbox.org/wiki/Downloads

[ download kali linux ova files ]
https://www.offensive-security.com/kali-linux-vm-vmware-virtualbox-image-download/  [old link]
https://www.kali.org/get-kali/#kali-virtual-machines    [new link]

Use the new link above and select the 64-bit VirtualBox torrent and use a BitComet program to 
download it.