Are you talking the lamp or the whole housing? Either way as far as I know the bumper cover needs to come off. Your car also has the option to have either hid or halogen lamps. They have identical housings. So you will need to verify the proper lamp. New hids are usually a couple hundred new oem lamps and replace in pairs only.
Try EBAY. I have been looking for aftermarket headlights for almost half a year for my 04 SRX. The only ones I seem to find are stock ones on EBAY that are from a Salvage Yard or a Used Parts store. I have been looking for a set with HALO's or LED's, but may end up having a local shop custom make some