wpcentral store for Lumia 1520 accessories :- Windows Phone Central - #1 Store for Windows Phone Accessories
or visit the nearest nokia priority to buy one from there , btw windows phone 8.1+ nokia cyan update will be available sometimes in this summer (May-June)
Don't they have some on display there? The two Microsoft stores here in northern Virginia have every color on display, and several associates use the phone themselves. But yeah, they're definitely nice and friendly every time I'm in there.