You are suffering from Elite Irony Disorder I'm afraid. It's never what you want. People think that this is down to rng, but really you are being suckered by the telepathic code that King Dave wrote into the program. Essentially, the game reads your mind, and predominantly throws up the absolute opposite of what you were actually looking for. But it does do it in a slightly helpful way, as they removed the part of code that meant you used to get fish out of some icy rings, and metallic would often drop battle weapons. Especially if the station you came from saw them as illegal.
Now, for solutions to this psychological telepathic problem. The best thing to do is to just fire off limpets at any and all rocks you can quickly fly past.
BUT, when you press the fire button, get used to the tiny pause before it launches the prospector limpet - this is the point that King Dave reads your thoughts. At this fraction of a second, you have to think of the opposite of what you could want to find, whilst crossing everything you have, and I mean everything.
For example, if you want void opals, think very strongly about getting water; for diamonds, think of bromellite. And so the opposite flows - if you want mmcs, think of opals; you want bromellite, think of diamonds. After all, they are a girl's best friend.
But you have to play by the spawn, unlike the old code. You can't be thinking of biowaste, or you'll get a bigass pirate. Think of narcotics, you'll get security ships.
So, it is all a bit of luck really, but the main thing is to spam out prospector limpets really, and cross everything - including your legs, and anything in-between. If you're a lucky chap, you could even try tying a knot in it, but I can't speak from experience on this.
I hope this helps in some way? If nothing more, than to make you smile at how much of a pita the rng gods are, and to make you really wonder about the evil code....
Good luck
