mikesgs300

Hello, I have a 2001 GS300 and I have been having some issues. While taking off from the stop the car hesitates and sometimes when coming to a stop the car will die. Also recently the cars RPM will lower and raise while driving on the free then back to normal after a couple of seconds. Can anyone help me with a possible fix. I was instructed to change the entire throttle body from lexus. Im also having trouble finding the throttle body assembly for the repair. Thank is anyone can help.