You can buy a physical CD that came with the game's PSP LE on XSEED's official web store for $5. Just follow this link and scroll down to the merchandise section:
You will, however, need to fill your cart with enough orders to put the cost over $20, though. You can also get the poster and bracer pin set from the PSP LE for $5, also. You can get other LE goodies from previous releases for $5,also, to fill up a $20+ order.