I've seen threads from people on another Lexus forum intent on getting a Prado rear door so they could hang the spare tire on it:
http://www.toyodiy.com/parts/g_J_2004_TOYO...1W-GKPGK_4.html I don't know why since the Japan market Prado rear door hinges have been reported to break from the weight of the spare tire.
Not sure if I chose the Prado that most closely matches your GX on the above website ... you could browse the Prado parts descriptions and drawings to see if there is anything you want.
I always dislike that Lexus cars have not had turn signals on the sides -- ones for the Prado are shown on the website above.
Also, replacement outside mirrors with turn signals might be available in the aftermarket in Japan -- over here people usually get the less desirable mirror housing covers with signal lights instead of the full mirror housing with signal lights more widely available in Japan.
Does your GX have the optional 3rd row seats? Or the hitch receiver? Here are the 04 GX specs so you can compare what was available to what your GX has:
http://www.lexus.com/cpo/model_library/GX/2004.html