How to find replacement for a discontinued thermistor component?
Low Cost, High resistance semiconductor thermal sensors at 300'C appear to be going off the market for various reasons.  Reliability being foremost.

Another e.g. http://www.digikey.com/product-detail/en/nxp-semiconductors/KTY84-130,113/568-3254-2-ND/1068979

Thin Film Platinum Resistor technology appears to be the best for automotive low cost, fast response, high-rel for EGR and other applications. Up to 300'C

e.g. http://sensata.com/sensors/automotive-sensor-darts500-e.htm  Custom parts are avail, if you have high volume demand.

If your volume is low with multiple sensors used, thermocouple wire and shared electronics could be an option or remote IR detection of heat radiation.