There are two small boxes containing numerous relays close to the right side of the battery (looking at the engine from the front). The starter relay is in the front box. It is near the front of the box.
This particular relay is blue in color. The part number is 28300-10020. It is probably used in Toyota models as well as Lexus models. You can probably get it cheaper at a Toyota dealer.
Don't just pull up on the relay to remove it. There is a small clip near the bottom on the right side which has to be released by inserting a screwdriver between the relay body and the clip.