2005 Escalade Radio Upgrade

I have a 2005 Escalade. The XM radio was removed by the previous owner and replaced with a regular GM radio (non-Bose brand). My onStar still works with the current radio. I have a separate 6 CD unit that still works and that is Bose. The original radio did not have naviagation, but it would be fun to have that too.
Where can I find a replacement Bose radio that does have XM and possibly the navigation screen? I don't have to have the navi system, but wonder if that would work in my car.
Thanks for any help!