Get yourself to a salvage yard. The odd vintage one will show up at charity/used shops as well. I think I’ve probably got a dozen or so legally obtained milk crates on the property right now, all from either of those two sources. Most are the durable, non bendy plastic, but we have a few of the old wire dairy gold crates too.
If you don’t want to search, or need a matching set, the container store frequently stocks a modern copy with the right dimensions and look but with none of the banged up charm. Still does the trick if you need a legally obtained milk crate in a pinch.
