"The Final Five" (Gozmol, Yellow Ledbiter, Gout Foot Johnson, Jonathan Muddlemore and Fearby the Prowler) are by far the most uncommon monsters. I'm part of a huge Achievement hunter group (600+ members) that have collectively ran the spawn areas of these uniques probably over 10.000 times. We were only able to find two of these unique monsters in one occasion.
All the other monsters/events you named are not all that uncommon and are found by our group on a daily basis. I can invite you to this group if you want, and you can get them for free when they pop up. Send me a PM if you would like this.