Call in, that's what I did. They'll look if it's in the system. They sent me to a store and initially that store said they didn't have it, but after prodding they looked and it was right there with the rest of the sprint phones.
For some reason, they told me that it wasn't released yet, but I said I called in and that it was already released. They checked the system and noticed that it was released, but that it also was pulled from the system with a potential recall. They sold it to me anyways stating that they can scan it and would work regardless. They also said that it may just be that because they didn't have their display unit out yet so it wasn't on the system to be sold yet.
But your best bet is to call the Best Buy and ask specifically for the HTC Arrive, nothing more. If you say windows phone it'll just confuse them. Say Arrive over and over and they'll just punch it into the system and see which store has them in stock.