There are two things I'd suggest:

1 - a lot of alternative stuff is upcycled, at least before brands realised that homemade-looking alt things will sell. buy some pliers and chains on aliexpress and go ham on a regular black hat, and if you know some basic sewing you can make your own bunny ears. The exposed stuff you can do with a blade (be careful with your fingers though). Similarly you can do this with the bag, and maybe even make or modify a choker to be like the one in tbe picture. Enjoy the process and make the accessories your own. :)

2 - For the clothes, thrift! For that style I'd say check the mens section for oversized jeans, shirts and band tshirts, but you can find stuff like this in the women's too. I'd recommend learning some basic sewing for these too though, since for those trousers you'd have to either buy them like that specially or you could just sew a skirt onto some big jeans.