Well you might have a couple of problems there.
You see, selling Mac OS isn't really profitable. I mean Apple does it but they are the creators of the OS. Every Mac comes equipped with Mac OS. It comes free with the computer. So the only time people buy Mac OS is when a new version comes out and they keep their old computer.
And than Apple offers the upgrade for a small amount of money anyway (under 10 pounds).
And I think to be able to sell Mac OS you need to become an Apple certified dealer. So you'd need to sell their hardware and other products as well.
As for selling Linux... That's even harder. Noone ownes it. It's licensed under the GPL (see
here for more info).
After all the Linux itself is only an OS kernel. The full featured version of the Linux OS is called a distribution. There are many Linux distributions and most of them (90%) are free.
Distribution is a Linux kernel, packed with a graphical user interface and software.
All of the commercial Linux distributions have their free versions.
Here are links to some commercial Linux distributions:
Welcome / Home - Mandriva Linux
Linux Operating Systems: SUSE Linux Enterprise
redhat.com | Home
Anyway, commercial Linux distributions are intended for large corporations or web-hosts.
And to tell you the truth I really don't know what would make me buy a Linux distribution since I can get them for free.