well what you're really looking for is Mac themes for the specific Window Manager you're using(or another window manager), you won't have much luck trying to find themes for "distros in general".
you could check out MLVWM
, but it's ancient and you'll have to hack out a config file. (I couldn't find any docs either)
is incredibly customizable and it can look pretty much like OSX, but again, you have to hack out a config (or check out fvwm-themes) to really get it working to your tastes. there are lots of config downloads, but using the fancier ones often involves more than just replacing the .fvwm2rc file.
you could search kde-look.org or gnome-look.org for "mac" and see what comes up - keep in mind that some items are just suggestions to developers though.
good luck, it's certainly an achievable goal.