i think you can get rare candies by giving shuckle an Oran Berry (specifically an oran berry), i have read about this on several reliable websites but never actually tried it.
you can't
buy them
you cant only if you have icheat or action replay
Clone them!
no
that's not possible
find them
you dont
there is no way to get 999 rare candys without gameshark or action replay.
yes, you go to solaceon town which you get to after you get mewtwo. you will see a house get some unowns and go in there talk to the person and he will give you rare candies for unowns.
you can buy them at battle tower
no. but there is one for 999 rare candies