I guess it depends where you are shopping. Through this site? I would say keep checking, most places of business can re-stock within a month or so. Some smaller businesses may take longer. I use a variety of different search tools to locate what I need. I also search smaller stores in the area where I am traveling and make a point to stop in and look around, even if I don't find what I am looking for I often find other things I didn't know I needed!
Thank you for your interest in our products. We have items that we sell out of continually and they come back into stock at varying times. Which books are you interested in that are currently out of stock? I can check for the availability of these books and when they will return to stock.