Where do you get Ditto in emerald?

after beating the elite four , go to fallabour city and enter the fossil maniac's house.... enter the cave behind the maniac and go straight to the center of the cave.... there you will find dittos which are lvl 35 and above..... if you go still forward you will get the other fossil which you did not choose..... ( if you chose root fossil you get a claw fossil and if you choose a claw fossil you will find a root fossil)