I recently held a lecture about 'How to be Kawaii' and for people who where there and other people here are some links to shops for brands and places to buy second hand along with two cheap full outfits and where to get those items! I will post more detailed information later but for now explore these on your own!
here are some japanese brands that sell kawaii clothes, a bit expensive but check them out!
if you like the brands above you can find them cheaper by looking for them second hand!
there are many more shopping services, these are the two I have used many times in the past but look around if there are options that fit you better! (I will write more about this later)
(Remember to change the currency to yen for cheaper prices!)
I will post more help on how to buy cute clothes in the future, here's just a link dump from things I talked about in my lecture!