I'm trying to edit the dialogue for when the player first meets atton and kriea

The find what you're looking for
and the Nice outfit lines to be specific.

But when I search in their dialogues, I can't find them. I checked the Dialog and the earliest one I found was when the player senses the droids in the other room. So where are the intro dialogues located? I'm sure I'll feel like an idiot after this, but its been driving me insane.

For you party members dialogues they's in the BIFs>dialogs.bif

For the dialogues that are specific to a module, you will find them in ERFs>modules

For a quick search, I recommend tk102's Findrefs: if you type "nice outfit" it will point you directly at the exact entry in the dialogue and it will let you extract the dialogue. (just make sure you check in the right boxes to get the search results you are looking for - read the readme)

the nice outfit is in the ERFs>modules>101TEL>101atton.dlg

Ah thanks. I was looking in the wrong modules area.