A wild latias or latios might be holding it, if you've got the eon ticket, you'll gain permission to southeren island where a latias/latios will be there holding a soul dew
EDIT:
however there is another method to get soul dew,that is to use GameShark
The steps...
1.Go to YouTube and type this in the search box,Pokemon Emerald-ALL ITEM on sale!!! (you can just copy and paste from here.The user is smarkoh)
2.Go click on (more info) at the description and the cheat is available there.
3.Pls rate and comment.
***The cheat is for ALL(most) of the items and it only works for emerald
Chat with our AI personalities
The Soul Dew is obtainable after getting the Enigma Stone from a Wi-Fi event that occurred in late August of 2010. When you take the Soul Dew to Steven in the Pewter City Museum, the stone will be examined by the scientist, and he will give you the Soul Dew.
Soul Dew is an item that can raise the special defenses and attacks when held. It can raise this by 50 percent.
Soul Dew is an event only item. They currently don't have any events that are giving it away. Currently, the only way to get it is through hacking.
Ask a friend to help you out on that mission
Capture either a latios or latias