Do linear thermistors exist on the market?
No, thermistors are always nonlinear. But RTD do exist and they are linear. They are widely used in industry as Pt100 100 ohm resistance at 0 degrees Celsius, since their low resistance are very immune to the environment noise, but difficult (expensive) to measure. On the other hand HVAC use Pt1000 i.e. 1000 ohm at 0 deg. They are easier to measure as Pt100.