Here's how you do it:
1) Slather a tree which is NOT the previous one you slathered, check back in six hours of game play and check if you got a muchlax.
If not go to step 1, if yes go to step 2.
2) Once you have encountered a muchlax capture it, then slather the same tree. Wait 6 hours, if you get munchlax again repeat this step again, otherwise repeat step one.
If you do not go to a different tree after failing to get a muchlax your chances are .01%.
If you go to a different one after failing to get a munchlax your chances are 1%.
If you do get a muchlax, going to a different tree your chances are 1%.
If you do not go to a different tree after getting a muchlax your chances are 91% that you will get munchlax again.
They are in the maniac tunnel.
You can only find Darkrai through a Pokemon Event.
battle island
You can find munchlax in the curl bay at the very beginning to your right.
You can only get Snorlax by evolving Munchlax.
To find a Munchlax you need to put honey on a tree, wait for a while and go back to the tree. You might find a munchlax but you can find other rare Pokemon too. Such as Aipom and Burmy.
underground. look for an explorers pack in Eterna city.
There is no person who will trade a Munchlax in Soul Silver. You have to breed a Snorlax with a Full Insense if you want a Munchlax.
Munchlax, don't try to "find out its riddle" it just a rock shaped as a munchlax that does nothing
You can slather some honey on a tree and it might come. (Munchlax is very rare though)
To find munchlax put honey on a tree and wait until a munchlax appears or breed snorlax.
Honey trees oh and let me recommend Pokemon platinum