Question:
Microphones in news conferences are often covered with very shaggy, cloth material.

Is this to reduce wind noise or voice pops?

Where are covers like this available for the Oktava MK-219 and other popular mics?

Answer:
Microphones in news conferences are often covered with very shaggy, - cloth material.
Is this to reduce wind noise or voice pops?

Wind noise. These mics are usually not used close enough to worry about voice pops.  Normally used on booms at a distance measured in feet/meters.
-Is this to reduce wind noise or voice pops? No, it's much finer than that.  It's like hair, almost.  It's to reduce wind noise.

Where are covers like this available for the Oktava MK-219 and other -popular mics?

You can get zeppelins from Rycote, which probably has a website at , I'd bet.  But it'll cost more than a 219 will, and if you have a wind noise problem you'll get more out of a microphone with a smaller wind cross section first