[color=magenta]Well, there are a couple of ways that you can go. You can catch an extra Ralts and trade it with a boy in Rustboro City for a Seedot, you can wait until you get to Fallarbor Town/Meteor Falls and look for the slightly more common Nuzleaf in the grass between Fallarbor and Meteor Falls and then break it for a Seedot, or else you can wait for TV to announce an outbreak of Seedot after you defeat the Elite 4.
Seedot is much rarer in Emerald than it was in Ruby. You can find one now, it just may require a ton of patience. You can find a Seedot relatively soon, or you could literally go hours and not find one.