As an LFS worker and manager, I can tell you special ordering is often difficult, depending on how the fish are ordered. If it's from a wholesaler, then it may be possible to get a few of a certain species. But if they're ordering direct from wild suppliers or fish farm like we do, then it's more difficult as the LFS can't order small quantities. Like say you want a few shell-dweller cichlids, we might not want to order them as we'd have to get 50, and they don't sell well. It's easier to order bigger, more expensive fish as the suppliers will often send just one.
If you're gonna do a shipped order, either order a lot of fish to make the shipping worth it, or split the order with some other people.