hifi-remote.com has upgrades for DVP-C600D and DVP-C670D, so we know which IR signals these use.  It is a near certainty that the C650D has the same IR codes.

Probably cheapest is a Comcast DVR remote.  Use setup code 20533.

Or get an Atlas cable remote using DVR 0533.  Similar prices.

If you want to splurge, get the learning 5 device RCA RCRP05B.  Also 0533.