pci fan controller

Is there a fan controller that can control a fan by reading the thermal diode embedded in the motherboard? I want to control a single 120mm fan that is right next to the processor heat sink. I also want to be able to program different fan speeds for different temerature values. I have been unable to find such a device. I assume that it would have to be a PCI card in order for it to be able to access thermal data from the embedded processor diode. The heatsink fan is connected to the motherboard 4-pin connector and I want to use a second 120mm case fan that is mounted right next to the heatsink as the major cooling fan for the heatsink (antec P180 case). I tried a fan controller with a temperature sensor, but it is difficult to locate the sensor where temperature values are accurate, and I want to be able to program fan speed to vary automatically with CPU temperature. I am surprised such a device is so difficult to find.