Where do you guys find free and usable box dieline templates?

I have been looking for good box dieline templates online but most of what I find is either too basic or not really production ready.

Ideally looking for sources that have a decent variety like mailer boxes, folding cartons and dont require a ton of cleanup before using.

Do you guys usually build from scratch or rely on template libraries and if templates where are you finding the ones that actually work?