I was just on MAC's website (maccosmetics.com) and noticed that they are now selling the pro palette refills online, along with the actual palettes! Previously you could only get these items at a free standing MAC store. This not only saves you money (refill pans are $11 compared to shadows in pots that are $14.50), but in my opinion, it's a much better way to store and organize your MAC shadows. No more depotting for me! The price of the 15 palette is $12 and the empty quad is $3.50.
There are also blush palettes ($12) that hold 6 blush pans ($15). If you guys have any questions, let me know!