Ugh I feel like new clothes that mimic early 2000's clothes never fully capture the vibe. Your best bet is honestly second hand sites but godddd it would be nice to find a store that CURRENTLY really gets the style right.
I honestly don't know where to find good stuff to mimic the 2000s, but I get most my actual 2000s clothes from thrift stores for pretty cheap and the occasional gift from relatives that were teenagers at the time XD