eCommerce (Amazon) returns.  These items come in their original boxes and are not mail packages.

I recommend the Party Box if you can swing it.  It's a large box filled will undelivered mail, unclaimed mail and overstock items.  Always a fun mix!

BupBoxes are a fun mix of undelivered mail, unclaimed mail and overstock items.  They also carry various other types of mystery boxes.

Mystery Boxes curate for resellers.  They have an Ecom box as well as Heath & Beauty and Clothing boxes available. 

Mail and Various Mystery Boxes of all sorts.  Their boxes change frequently so keep checking back.