I think Brad might have been a bit confused when he replied to you... you've already got the lights, and now you just need the softbox, right?
Just to get it out of the way... Alien Bees (Paul Buff, Inc.) accessories do not fit on Novatron heads. Different sizes.
Photoflex offers a complete line of softboxes that are reasonably priced, built well, and will fit the Novatrons with the appropriate speed ring (and adapter that fits different heads, allows you to turn the box from horizontal to vertical, and all angles in between).
Photoflex web site - has some interesting "how to" lessons as well as lots of goodies
I've been using a large Multidome box for over 15 years, now, and with all of the packing, unpacking, setup, teardown and ignoring it in the carrytube for years at a time, it's still working just fine. Consider that an unmitigated endorsement.
There are other softbox manufacturers out there.. including the no-name or off-brand. Some will steer you to places like Amvona, which sells primarily online through eBay... after seeing a couple of their softboxes (and this applies generally to the off-brand stuff) think about how long you might want to use the equipment and invest accordingly.
Good luck and enjoy shopping!