Search the forums, people are always dropping good mining locations, double hotspots, etc. You can also use EDDB.io to find likely planetary rings, take a bit of time to figure out how to make EDDB work for you though.
Just so you know, VOpal is not the easy money-maker it was a year ago. Mining in general has been nerfed pretty hard over the past several months. I used to pull down:
in a single trip but mining has not earned that much in a long time.
A little more work involved. But I've had more success tracking down low traffic systems whose rings display less if any evidence of smashed 'roids where the goodies used to be...
Previous comments about the current nerf mess in mining apply. My last Void Opal run in my Python gave 192 tons and a full refinery hopper with 10 tons ore. Five hours work and 331 MCredits. Be prepared to haul your hard work some distance to reap a good return...