Those "issues" aren't really issues. Looking at my mac keyboard (old white/clear board), the number pad doesn't have navigation commands on the keys and therefore has no need for a numlock, as the numpad is JUST a numpad and there is no scroll lock at all on the keyboard.
One issue you *might* have is if you are used to the old desktop mac keyboards, that have F13-F16 and a dedicated Eject button.
If you worry about muscle memory issues, just go into system preferences and set Alt to Command, Command to Alt. That puts the keys in the proper place. And on some mechanical boards, you can even swap those two keys, so you don't get confused.
But as iMav said, it's quite easy to use even an old keyboard, such as a Model M, on a mac. As apple likes to claim so often, it just works.
My advice is just get one that you like the feel of. Don't worry about compatibility at all, because it's a non-issue. There are even some keyboards that have MORE functionality when attached to a Mac, such as the HHKB.
Edit: I'm not sure what makes the Unicomp explicitly mac compatible. It's identical in functionality to pretty much every other keyboard.