Be careful what you r looking for. This is not a flame sensor. Its a main limit switch, adjustable 120-250F with a fixed differential of 30F. They must be replaced with the OEM part. Match the temperature setting of the old part and test it, make sure it operates properly. Limit switch should shut the burner down no later than 3-3.5 minutes after the main burner ignition, when the blower fails.
Cam-Stats are still available, you should be able to get the same part.