1. u have to run into them by luck so u can track them down in ur pokedex
if the pokemon runs away, don't worry, u r able to track them down
2. get a haunter with the move mean look and hyponis(or another attack with good accuracy and sleep effect)
3. put haunter as ur first pokemon in your party
4. go to any grassy area where u can encounter pokemons
5. check ur pokedex to see where the pokemons r in
6. keep entering a house then get back out
possibly, the pokemon should have moved to another route
keep doing it until it comes to u
use repels if ur impatient
7. when u encounter it, use haunter's mean look
8. use hyponis
9. attack it! (don't kill it though)
10. ultra balls! go!
if u have a masterball duplicate it and use it on them
u can duplicate it by doing the following steps:
save in front of pc
deposite the pokemon holding the masterball
change box
when it says "saving... don't turn off power..." turn the gameboy off
turn it back on and u'll see that u still have the pokemon with the masterball in ur party
look in ur pc and u'll find the same pokemon holding masterball with same level and same stats!

Look all over Johto and hope you run into them in the wild
also after you battle them the first time, you can see where they will
be next but dont knock them out cause then they wont come back.
Use either mean look or spider web against them.

Quote: speedster821

I can't catch them cause when I try to weaken one of them, they run away. I can't make them fall asleep either.

caughgt suicune i weakened it and i caught it with no trouble