My local Woodcraft no longer has any sort of decent selection of thin wood. I have been buying from Ocooch over the past year and have been very pleased with them. I've only had one bad board from them and when I called, they replaced it. I have spent a lot of money there since! Even when the Woodcraft did have thin wood, you never knew what you might find when you got there (and it's a 20 mile drive for me). It is nice to be able to just go online and specify a width, thickness and species and find it on your porch a few days later. I do try to buy in bulk to save on shipping.
This post refers to hardwood, not ply. I don't use much plywood generally.