Believe it or not, places still exist where you can physically walk into a store, pull out your wallet and leave with a part. And like swap meets, one big advantage of these brick-and-mortar stores is being able to talk with experts about what you need and how to get it from the shelf into your ride. The disadvantage, of course, is that the store may not have it. Call ahead with your make, model and year to ensure you're in the ballpark.
One last word on shops: The unspoken rule is that if you use the expert, buy the part. No fair extracting advice and then going home to search for the part online.