I'd look at what Robert Bosch can supply for engine monitoring - they have a wide range of sensors for pressure and temperature, even on the exhaust manifold. Otherwise, depending on your required final precision, a type N thermocouple and a T/C amplifier from Analof devices should condition your temperature measurement just fine.

There are off the shelf T/C amplifiers, with voltage outputs available. What kind of production quantity are you looking at ?

Steve