This is one that really bugs me. In my (limited, admittedly) experience with retail, if I didn't know what something was, I'd make an effort to find it. Not all the stores in our chain had the same stock - and some stock was advertised on the website but not available in stores for reasons that were never rectified, but I'd always pull up the website or check for codes to find what they wanted and if we could either order it in, or direct them to another store within walking distance (after phoning to check their stock, of course).
We were lucky that we had that system, but (at the risk of becoming an old man ranting at a cloud) the younger generation couldn't be arsed with it, nor would they read the morning updates we'd get on stock. Doesn't take much effort to work with the customer instead of disregarding them.