You can find them by driving around. Emergency events don't actually change unless someone completes them, so staying in one place might take a while. Personally, I've ran into quite a few Volge around central Sausalito. Also, San Francisco is packed with Volge emergencies. Good luck. --- everything is fire http://steamcommunity.com/sharedfiles/filedetails/?id=131193830
You want to draw out the Vulge and try to isolate them if you want to solo (decoy helps a lot here). Don't take them head-on, since they will destroy your shield very quickly with their rapid fire.
Also, the elite Vulge has a very easy pattern. When you see his arm glow red and pointing at you, he is going to fire his cannon that will one-shot most people. If you see him glowing blue, it means he is going to charge at you. Both are easily avoided by rolling sideways.