The trouble with junkyards is that they sell material that's usually damaged in some way, and they don't necessarily know what it is. And surprisingly, it's not always cheaper than brand-new material of known composition. You just have to be ready to buy a whole piece, if you're buying it new. Some places will cut things to size for you, though, like TCI in Hayward Custom Metal Cutting, Metal Finishing | Aluminum Supplier & Precision Machining - Hayward, CA and Maxx Metals in San Carlos: Maxx Metals