Just about every home center should carry 10" wood planks. It really depends on what kind of wood you're looking for and what you'll be using it for. Right now the closest home Depot to me has a couple of different grades of 2x10 in douglas fir and they would happily cut it to 46" for you, but like 2x4s 2x10s are actually smaller than their advertised, I think a 10" board is really 9.5" the grade of wood at big box stores is generally not well suited for anything but construction. If you're looking for something exactly the dimensions you need or a different type of wood I would Google around for a lumber supplier near you, they typically have all kinds of wood and can cut it to your specific dimensions. In my experience, if you want something nicer than construction lumber you should find a lumber supply company.