Your best bet is either to contact some of the bigger and more reputable car audio installers/suppliers or try some of the specialist electronics places like JayCar, etc.
Finding a fold-out screen is easy, and there are plenty around from Alpine, Pioneer, Kenwood, Clarion, Sony, and some of the smaller brands like NESA, etc. Then it's just a matter of finding a navigation set-up to suit.
Most of the navigation stuff here is of the stand-alone variety, like the NAVMAN, ToMTom, Garmin, etc. The one in-dash one that I can think of available here is from VDO-Dayton, but even then it would take up two DIN spaces, unless you mount the control box with the DVD or CD reader (depending on your choice) under your seats.
Alpine do have navigation stuff available, but it's o/seas only...