One of the neighbours in the intro (forgot her name, I think it starts with A) is wearing a green floral skirt with a belt.

I want that outfit but I'm not sure where to find one in the game?

I don't know, sorry. What you could try is building a clothing store in your settlement (if you have the Local Leader perk). It's supposedly a seperate store from the armor vendor so they should have a good amount of clothing in stock.

Thanks, I could do that.

Failing that, I can wait for the GECK and console spawn it.