In many places, I have seen green USPS curbside collection boxes.
Traditionally they are thought of as blue, like the ones seen here:
http://www.whbvillage.com/images/usps-boxes.jpg

However, I am interested in finding out the places in the United
States where the collection boxes are green (by zip code, city, or the
narrowest location category possible). Where are they green?

Howdy macromicromini-ga,

As nelson-ga points out, the olive green boxes are not collection boxes, but
rather they are "drop" or "relay" boxes.  We can reference the U.S. Postal
Service (USPS) Publication 32 "Glossary of Postal Terms" for details.
http://mailservices.ucsf.edu/pdfs/USPSPostalTerms.pdf

"drop box ? The olive green noncollection receptacle where city carriers
leave mail on the line of travel for later pickup and delivery by another
carrier. (Also called relay box.)
...
relay ? Mail that a city letter carrier prepares in sacks for delivery to
relay drop boxes along the line of travel of a route. After completing
delivery of carry-out mail, the letter carrier picks up additional mail
from the relay drop box and resumes delivery, continuing this process
until the entire route is served. A relay may weigh up to 35 pounds.
...
relay route ? In city delivery service, a route in which the city carrier
places sacks of mail in drop boxes for pick up by city carriers as they
deliver mail on their routes."

You will still see relay boxes in urban areas, but as more letter carriers
are using vehicles, they are in declining numbers.

At one point all boxes, drop/relay and collection, were olive green.  This
model makers discussion on the ?HO Sam? website covers this subject.
http://www.hosam.com/misc/mailbox.html

"Olive drab starting in 1909. On July 4, 1955 the Postmaster General ordered
them changed to red, white and blue. In 1970 they changed to solid blue."

As one might expect, the olive green paint originally used was sourced from
the U.S. military.

This Google Answers question, "Where can I buy a real USPS mailbox?" might
interest you.
http://answers.google.com/answers/threadview?id=461674

If you need any clarification, please feel free to ask.


Search strategy:  Personal experience.

Google search on: USPS "relay boxes"
://www.google.com/search?q=USPS+%22relay+boxes%22

Looking Forward, denco-ga - Google Answers Researcher

Thank you for the excellent answer. And it is fitting that you would
refer me to the question on "Where can I buy a real USPS mailbox?"
http://answers.google.com/answers/threadview?id=461674; I know
wunderkind-ga very well (who posted a comment on that question), and I
am actually still trying to accomplish that task. If anyone knows any
information on that ultimate question, that would be most helpful.

Thanks for the great glossary -- it will come in handy.

The green ones are not collection boxes.  You cannot put mail in them.
 I'll let a researcher give you the specifics and collect the $15.

Thank you-- yes, if a researcher answers the same, of course I will
pay the $15, but since you know, what are the green boxes for? Are the
USPS operated?

Thank you for your help.

Much thanks for the 5 star rating, kind comment and nice tip,
macromicromini-ga.

I think your best bet, as suggested by your friend wunderkind-ga,
might be the USPS at one of their disposal sales.  Here is some
contact information, but as it area specific, you might want to
check it in detail.
http://www.usps.com/consumers/business/pmsc_print.htm

"For information regarding auctions and sales to dispose of postal
equipment ..."

Looking Forward, denco-ga - Google Answers Researcher

If you're looking to purchase an actual mail box, you might want to
try a theatrical prop shop.  They have all kinds of stuff you might
not normally be able to get your hands on, and depending on what kind
of money you're willing to spend, will probably be willing to sell,
rent, or share their sources.  I don't have any off of the top of my
head (although that would make an excellent question for one of the
researchers) but here is an great book that I used to use when I was
in college working in the school prop shop.

http://www.dramabookshop.com/NASApp/store/Product?s=showproduct&isbn=1557836914