this is simple. Your own trunk!!!!!
Take the scratched up rim (assuming it still runs true and balanced) and make it your spare. The spare that is in you trunk is a matched rim and looks just like the other 4 on the car.
If you are concerned about the uneven wear, go to a tire shop and have them swap the used tire to the unscratched rim and the unused spare to the scratched rim.
Other than that, ebay or a junk yard. On line Lexus dealers sell them for about $300, more for the chrome.
steviej