Kinda a hard nut to crack at first, but once you do you'll know why... info on these auctions are hard to get and therefore hardly attended. That leaves a few containers for just a handful of buyers to bid on (i.e. low competition).
What I did was went to Google Maps and searched near my location with terms like "container storage", "container rental", "mobile container", etc... that will turn up business names in your area. Then it is up to you to call them and acquire info about their delinquent rentals.
Conversation usually goes like this:
Me:"Hi, I was told that you auction off the contents of your delinquent accounts... I would like to inquire if that is true, and if so, find out if I can be placed on a list to be notified when those units come up for auction."
At that point, management will say that they don't do rentals (something you should've verified) and therefore don't auction off delinquent accounts or that they do conduct auctions and will then help you obtain the info you need.
My experience has been mixed: 30% put me on an email notification list, 10% say to just check the website, and the other 60% I haven't lasted long enough through the large automated phone service to get the answer I need.
Hope that helped.