This is an "off the shelf" panel and so you cannot order it customized to your specifications. It is set up with six empty slots and the idea is that you would order six breakers and mount them yourself before installing the panel. (Its easier to do this before all the wires are attached)
If that doesnt work for you then you can go with a custom panel which you can design yourself online using the Panelwizard program. For custom panels you can spec everything out yourself.