Sorry for this n00bish question. I haven't been on Subeta for AGES.

Where is the Unknown Island located nowadays? I can't find it on the (new) map.

it's called Omen Islands, but you won't be able to get there until the plot's finished.

Oh, okay. But then I will still have access to it? I completed the treasure map long ago and I want to re-paint one of my pets Hydrus.

If you completed the uncharted lands map, then you can go directly to Merana to get a Hydrus pet.

http://www.subeta.net/explore/merana.php

Amazing! Thank you :)