Sites like Etsy and Amazon are excellent for sourcing furniture-grade hardwoods like black walnut or live-edge slabs that big-box stores typically don't carry.
Home Depot and Lowe's are the most accessible for "appearance boards"—wood that is already sanded on four sides (S4S) and ready for a finish. They offer common species like pine, poplar, and red oak. where to buy wood planks for shelves
Solid Black Walnut Shelf – Furniture-Grade Plank, Wood Board for DIY Shelves, Handmade in Quebec Sites like Etsy and Amazon are excellent for