Where does everyone source their custom branded packaging from?

Trying to figure out where to get custom branded mailer/shipping boxes made in decent volume (a few thousand units, recurring). Not sure whether to go through a supplier, straight to a manufacturer, or overseas — curious what's actually worked for people here.

If you've done this before, who'd you end up going with, and would you do it again?

I've spent a good chunk of time going down this rabbit hole myself (vetted a bunch of manufacturers, got quotes at different volumes) so happy to compare notes if it's useful to anyone mid-decision too.