any auto parts store: auto zone, pep boys, advanced auto store, etc.
If it is a bulb, yeah, your owners manual should show you how to replace it, but if it an LED group then the only way you are going to get one is from a wrecking yard that has a similar model. Do you understand what I mean by LED?
u can check ebay, autozone or amazon. http://lexusgs.org/
Looking for a Used GS 350 in your area?
CarGurus has 3,581 nationwide GS 350 listings starting at $5,995.
Search Lexus GS 350 Questions
Lexus GS 350 Experts
Related Models For Sale
Used Cars For Sale