L.C.
I have a RCA radio/CD player clock for my daughter. What I love about it is that I can set it to play repeatedly. It does have a sleep mode where you can set the radio/CD player to turn off after a specific time that you set. You can set it as low as 1 minute to as high as 2 hours. When you use the sleep mode for the CD player, the CD will automatically play over and over until the sleep time has been reached. I believe this is what you need.
I believe I bought it at Target. It is by RCA and the model is RP3765.
Lullaby CDs can be found anywhere, but better choices at Babies R Us.