if your looking for bulbs.. most stores that sell them will have a book that you can look up your year make and model of your car. then all you have to do is find the part number that fits your car.
if your looking for the entire euro lamps, like the whole light assembly then you would just need to know your year make and model. most stores that sell them can help you find what you are looking for. if you are looking online most are organized by year/make/and model also.