Where can I find this flooring?

I would love to redo the flooring in my study. Right now there is carpeting in there, since the people who owned the house before us used the room as a bedroom. My chair won’t roll on carpeting though, and the carpeting is all worn out anyways. I was thinking that it would look nice to put antique oak flooring in there. Where can I find this type of flooring? Do I have to go somewhere special, or can I just go to one of the chain home improvement stores and ask them about it? Is it really expensive to install?