Air Speed Measurement Sensor

[kamocat]

How about creating your own?
You can measure deflection with a piezoelectric crystal.
You could also measure static discharge to the gate of a transistor (generate a steady electromagnetic field on the end of the material, and put an antenna on the gate, so as the field nears the antenna, a greater amount of energy is discharged to the antenna. Make sure to sink the antenna with a resistor (100-megaohm), because you will need fairly high voltages to have noticeable effects over air)

Or you could put an optical encoder on a pinwheel.
Or measure the pull on a strip of silk. Actually, you could might be able to follow the currents with this, too.

It sounds like you need measurements down to 50mm per second. Unless there's something that responds on an exponential scale, I think you're going to have trouble calibrating it. Accuracy is a very difficult thing.

(Considering it's around easter, you could probably tie tufts of easter grass to floss instead of using silk)