I bought a reader with a damaged screen and scavenged the casing.
It's just a matter of disconnecting a single ZIF connector (the big cable connecting the casing to the MOBO), slide out the mobo and slide it into a new casing. Reconnect the ZIF connector and you have a new casing..
There is a thread on the flea market section
marked Five PRS505 & PRS500 for spare parts, 2 good screens ( 1 2) where you could inform for a new casing.
I paid 75 dollar including shipping for a broken screen reader, send to me in europe, from a forum member in Japan....