It blows my mind how many people say "bookstore didn't have it, I guess I can't buy it."
Ditto. i've been "grooming" bookshops since December 1979. I befriend their SF specialist, let them know what interesting SF media stuff is coming, and I make a point of telling certain shops if i've had to buy elsewhere. And I tell them when I've brought in a friend to browse their stock, and make sure the SF person sees that my friend is buying something.
When you "special order" an in-print ST novel, the shop will often order a few shelf copies at the same time, and then you're helping out other ST readers.
There are only so many shelves for so many books. A shop is likely to get in 40 of the latest "Harry Potter" and ten random single issues of ST titles. It has to be a mighty big shop (or an SF specialist) to think of getting in ten of each ST title just to have them sit on shelves "just in case".
Actually, I was very pleased with the number of general bookshops in Sydney that had 20 or so copies of the Alan Dean Foster novelization of ST XI! And most seem to have sold now.