i am not a gyaru but ive seen lots of gyaru clothing at thrift stores such as leopard print items, jean short shorts, bright tops and purses. id also recommend garage sales and they usually sell them real cheap. for accessories, id say do some online shopping bc idk much about that and makeup but here's some videos to help you
https://www.youtube.com/watch?v=lpQaixgjVX8&t=207s
https://www.youtube.com/watch?v=kHJ_umef2ms
https://www.youtube.com/watch?v=YOySlLBF1cg
I hope that this helps you!!!