First. I'd report any employee at Home Depot or Lowes who showed displeasure with me trying to find decent wood. Fact is, they should be helping you. On the other side, since it's convenient and usually a reasonable price you can sometimes figure out if you can cut around flaws. Not the best answer, but if a sheet is decent and I know the dimensions can be cut within the "good" wood then it's a choice I can live with. YMMV.
Second. If you're in or near a many major city, see if you have a MacBeath (sp?) Hardwood. They also have sheet goods. There are a lot of sellers to cabinet shops that will sell to the public. I've done this with hardwood, but not sheet goods. I've also gone to a local cabinet shop and ask them to add my order to theirs as I live outside of town and a delivery to my house could cost a bit. As the cabinet shop orders in bulk they are not charged for the delivery. It pads their order and I get delivery up the mountain.
Finally. Online sellers are usually willing to assure that their products will be decent. Being able to check grain, etc can be a limitation, so take that into account. Talking to the person who is selecting your order and telling them what you're building and they often will take some care in selecting your order. I have not done this as I'm bit skeptical that the shipper will take care not to damage the edges.