RNG seems indeed to be the answer. I got all vile bloom souls at 886 kill count - and I know precisely because I haven't killed another after that, still my kc
I can't however for the life of me get a single totem piece from big game hunter after lots of hunts and having trouble with ripper dino soul and the piece for slayer lodge 3. So hang in there and better luck!
Also as a side note: bad luck mitigation - developers, add this to everything you can please.