Pastels are great for Fairy - Kei. But it's hard to find the clothing you like that are pastel and can pass for Fairy - Kei. And you don't necessarily have to be right on target with the whole "Fairy - Kei style", as long as you're having fun then it doesn't matter what others think. You could even create your own unique style.
Some good places to search is Walmart - Ebay - Thrift Shops - Etsy - And so much more...
Walmart has some good tops, and even some nice pastel shorts. My last visit I got a mustache tank for only $3.88. The colors are a bit lighter in person and will get even lighter after a month or so of washes.
Ebay always has some exciting things. I found a light blue cardigan for $3.99 and it looks new. Just add a bow and sew on come lace for decoration and it would look so pretty.
And again at another Thrift Shop close to home I found a few pastel shirts. Pink - Pink and white striped - and a Lavender. Two of them new with tags. Spent a total of $11. Which I think is a good find.
You're not always going to find things. But if you are patient then you can find some pretty good things! Good luck with the hunt. (: