I don't know about the other floors. When I had that much trouble inside the mountain, I just went outside instead and that's where I do most of my RNG now. What you could do is just test the encounter slots, stop at different frames with the correct IV spread and see what you catch until you find the right pokemon, hopefully. I've had to do that occasionally, for head butting mostly.
Yeah, I had no trouble in the grass patches outside the mountain, but Misdreavus isn't out there. Thanks for the advice though :)
Most of the Mt. Silver encounter slots don't match up with the appropriate map that you're on. The Psypokes maps don't match up with the actual floors that they are.
Just keep on trying on different floors. I think I found my encounter slot 7 Misdreavus on floor 3F of those maps (in reality not 3F but w/e).
Alright, I think I'll try that next then. Thanks :)
Edit: yay, it worked! :D