You could download the .deb file of it and install it via dpkg -i .
Also BT is not a distro for everyday's use (if you are not a pentester ) Or just try to experiment a bit for yourself. The worst thing to happen is that you have to reinstall it.
Or you could run it from a live cd, try to add the repos and then do it on your live system. Also I'd not recommend necessarily to add the Buntu repos since they might mess up something.