Edmund Scientific has wind gauges. Also, you could take a PM (Permanent Magnet) motor and mount a small hand carved prop on it and put the output wires into a panel volt meter. They will put out a DC voltage when you spin them, so, they can double as a generator. To calibrate it to mph wind speed hold it out a car window while a friend is driving and mark the volt meter in 5 or 10 mph increments. That's the best I can offer for homemade. I have been doing a little experimenting and I found an old heater blower motor I had replaced because it was stuck. It was easily repaired. It is of the newer type that is not made to be taken apart, so I worked it a little and it seemed to free up. I shot WD40 in both sides to clean and lube the bearings. Seemed to do the trick. Wired it to a battery and it ran very well. Must have had a bug nest or other dirt in there clogging it somewhat and the garage replaced it rather then messing with it, you know, It came off my wife's '89 LX Mustang. Next, I wired it to my volt test meter and connected my hand crank drill to the shaft via the chuck and cranked it gently and I was able to generate DC voltage. So it is a PM motor as I had suspected. I like the mounting flange around the middle with 3 screw holes for mounting. I think I have a good possible wind generator here.
Offered by Darrell.
Hook it up to a small propeller or a homemade, vertical, small 4-cup type windmill. Good idea you have about how to test it using a car and holding it out the window.
Offered by Mike.
I would pick up one of those small toy cars that run off a couple AA cells. Remove the little motor, and you have a very small DC generator. I would also go to a hobby store that sells the remote control airplanes and pick up a replacement propeller. The mounting hole will be too large, so fill it up with something that will set like epoxy or silicone. Then drill a hole the size of the generator shaft and superglue onto the generator. I built one of these about 20 years ago and after calibrating the meter it is quite accurate. Actually, you don't need to mark the calibrations on the meter itself. Just make a table. One column is meter indicated voltage, and on each row place the wind speed. I find this method to be very accurate. You will find that the function of voltage to speed is not linear because of the propeller characteristics.
Offered by Ron.