Geeetech

I have a prusa I3 pro B printer, and I have heard that extruder cooling fans can improve print performance of plastics like PLA. Where Do I get them and how do I install them. thanks.

You can find fan ducts on thingiverse.com. Just pick a style that works for your printer, you can buy fans online.
Here is one that I used when i first got my printer, it clips onto the heatsink and doesnt need another fan. That gave me better quality and let me print a better duckt to work with a seperate fan.

Clip on Fan Duct
https://www.thingiverse.com/thing:1872654
https://www.thingiverse.com/thing:1243891

Duct for radial fan
https://www.thingiverse.com/thing:1540434

Hope this helps

Adding fans is a good idea to improve the printing quality due to its effective temperature controlling，
here is a link introducing the material you need to assemble the fans and the assembly method of the video.
/www.thingiverse.com/thing:1716276/#made