I need to obtain a XG1v4 box

I have 2 set top boxes. One is a primary box and one is a secondary box, which requires the primary box to be present to work. I have replaced my primary TV with a new 4K TV and need to obtain a XG1v4 4K box for that TV to replace my primary box. I also need to replace my secondary box, since it will not work without the primary box. How can I obtain new boxes? Is there a monthly rental fee for the new boxes over and above what I am now paying for my current boxes?