Newegg.com and geeks.com. The second place is discount so stuff comes and goes. You are unlikely to find such at retail outlets.
Ok, somebody help me out here. When you buy a digital camera, they don't sell 2 MB, 4 MB, or 8 MB cameras. You buy a camera for it's features, then separately buy as much or as little storage as you need. It's the same with virtually every other piece of electronic equipment, except for MP3 players. Whenever you run out of storage and want more, you need to throw the baby out with the bath water and buy a new player.
Why not have an inexpensive but feature-rich player that comes with no memory and a micro SD slot? You could expand its capacity as much as you want, split your music acrosss multiple SD cards, even share one player among multiple family members. Why don't they make something like this?