Temperature sensor are needed to compute True Airspeed for low speed aircrafts?
A good chunk of aircraft operating in the &lt;100Kt range generally don't have Air Data Computers although glass cockpits are becoming more and more common in general aviation aircraft. For good old steam gauges a sliding temperature compensation scale is built right into the Air Speed Indicator, for more info on that see this question or this video. OAT is determined generally by a thermometer installed on the windscreen or in the side window.  

If your aircraft is equipped with with a capable glass cockpit you may be able to get TAS from the system 


  The Airspeed Indicator displays airspeed on a rolling number gauge
  using a moving tape. The true airspeed (TAS) is displayed in knots
  below the Airspeed Indicator.




The G1000 has an OAT gauge as part of the install. 


  The Outside Air Temperature (OAT) and the deviation from International
  Standard Atmosphere (ISA) temperature are displayed in degrees Celsius
  (°C) by default in the lower left of the PFD under normal display
  conditions, or below the groundspeed in reversionary mode.