Here is a link to the wiki:
http://lastmoon.org/wiki.phpIt will tell you were everything in the game spawns. Some creatures are rare spawns so you have to re-enter the map a few times.
Dimension hopping allows for easy reloading of a map, to do this you press H to bring up the home window. You will see Dimensions listed there (usually set at 0). Click the Change button and type a number ranging from 0-9, this will change your dimension and reload the map. Stay there for a few minutes to see what spawn and then repeat the process if you can't find your prey.
I know some creatures are really annoying, like the Monster Cow, have only seen that one twice since I started the game.
Further, star dragons aren't very rare, do the Dim hopping technique explained above while you are in the Jungle map and one should spawn soon.
Taming on the other hand is hard, you have to lower the beast's health, then use tonnes of tames on it. Each time you use a tame you have only a small chance to tame it. Rather buy a Star Dragon with gold medals at the Bazaar, they are at the Boss and Praise pet NPC.