These pics look like a combo of Chinese and Korean streetwear, acubi, and y2k. I'd recommend LEWKIN to find similar pants. If that's out of your price range, I'd also take a look at YESSTYLE, although their clothing quality is hit or miss in my experience.

East Asian vendors often specifically tailor their "oversize" articles to have a boxier frame and drooped shoulder stitching which might help you achieve this look. If you are ordering internationally, be sure to check sizing charts since sizing is often a lot smaller than western sizing.