If I remember correctly from aerodynamics lectures, there is no other reliable way to measure airspeed.
One could use Doppler radar, but that would involve tracer particles. Or one could use a propeller which might give somewhat reliable readings below 300 knots but would completely miss static air pressure.
There most certainly are ways of measuring gas flow velocity; there is a huge industry making sensors which do this. Ultrasonic, coriolis, you name it. The raw data will not be the same as a pitot tube (which doesn't measure TAS anyway) but could be corrected back to read an "IAS" like a pitot tube does.