Have a new 4K set on my account, but I do not have a 4K box and was wondering how I would go about obtaining one.

I recently purchased a new 4K TV to replace a 1080p set that died in one of our bedrooms. This is the first (and so far only 4K set in the house), so I hadn't needed to be concerned about the main box being able to produce a 4k signal up to this time, but now that I do have one 4K set I'd like to be able to see cable broadcast in 4K on it if possible. Thanks for any help that  you may be able to provide me.