Q: Can I find larger sizes clothes in Seoul?
Many shops are selling free size but their definition of "Free Size" may be different from yours.
For the current trend (ladies), these fashion are quite suitable for larger sized customers. I didn't find it difficult as there were some shops selling just for larger sizes and I saw those in many locations. The only problem I found was the pants - I couldn't fit in some of the pants for UK10.
For men's clothes, I couldn't find the common western XXL. I visited many shops and Korean's XXL were like L to me.
Just be aware that it is common for the shops (not referring to the high end/ department stores) with "No Fitting Room" policy since they are selling free size clothes, what you see is what you get. Having said that, I found some retail shops actually provided fitting rooms. If you are just shopping for the high end fashion, you most probably do not have this problem.
A country rich in history, culture. If you have never tried the delicious Korean food, it's colourful culture, or perhaps check out the plastic surgery industry - this definitely is a popular destination for Asia.