Not all the planets with ring(s) have RES
There some great places like Leesti
Is just a problem of whether you would like to move house or not.
In my experience so far, you have a good chance of finding an RES when the following applies:
-The system features an extraction and/or refinery economy (at least on some or most of the stations)
-The system has at least one planet with a ring system that is either rocky or metallic (click the planet on system map and check)
For a good RES hunting ground you'll want a station, better yet an outpost, in orbit around the same planet that has the extraction sites in its ring. If you also like to run missions, you'll want the planet to be as close to the primary star as possible.
I don't know whether the security status of the system plays a role in the frequency of pirate spawns in extraction points, too, but as a bounty hunter, you will generally want the security level of the system to be as low as possible. And don't forget the KWS, especially when it is an anarchy system
