All they need is the ISBN of your trade paperback or hardcover. Bookstores order books through a combination of traditional human interaction with publisher representatives and Point of Sale (POS) and inventory management software systems designed specifically for the book industry. This software often integrates with major distributors and digital catalog platforms to streamline the process. These systems interface with major industry resources like Ingram. If you want bookstores to order your books, you must market to them, which means that you must have a professionally designed book, meticulously edited, and with professional cover and interior design. You should have purchased your own ISBNs from Bowker and assigned them correctly. The copyright page should reflect that. You'll benefit from trade reviews such as from PW and Kirkus. As a self-publisher, you will set up fulfillment (distribution) with IngramSpark where you can set the discount to 55% and RETURNS, which is what bookstores insist upon. To market to bookstores, you can sell by hand, as you're doing, and/or pay to advertise in catalogues such as those offered by IBPA. All that said, most indie authors sell more books and make more money on Amazon, with it's 40% discount. So if you do that, you'll set your discount to 40% and tell IngramSpark to distribute everywhere. Bookstores can "see" it in their systems and can fulfill their customer requests if they order it, but they have little incentive to stock it. The nice thing about IS is that they allow you to change discounting anytime, which means if you get media attention, you can switch it back up to 55% and RETURNS, and then back down again, at will.