Here's a link to a business that is reselling bar codes/UPCs. It is one I described above as having a large block of numbers that they purchased prior to 2002 when the laws changed. It has really good, easy to understand descriptions. This is the home page link, and check out their FAQ's also.
Their prices start out at $22 per code and go down the more you buy.
http://www.iwantmybarcode.com/index.htm
There is references of Large Retailers who won't accept products that have re-sold UPC numbers. A little research found this text from another UPC seller-
"You are made aware that some Wal-Mart stores or regions, some Kroger Grocery stores and possibly Wegmans Grocery stores may not possibly accept your subset UPC because it is not purchased through the GS1 and they require your own unique GLN and GS1 certificate.
(We think it's interesting that officials from Wal-Mart and Wegman's are on the governing board of the GS1). These are the only three retailers we are aware of that may not accept your UPC/EAN subset number as they may require you to have your own costly manufacturer's number certificate that you can only obtain through the GS1, however we also have reports of people successfully providing UPCs to these stores and not being asked for a GS1 Certificate. If your product becomes so successful that you obtain a distributor who wants to mass market your product(s) in those stores, then your success at that point ought to justify the high cost of obtaining a manufacturer's prefix through the GS1. For everyone else, EZ UPC is an extremely easy, legal and affordable solution. Your worst-case scenario is that you would have to get new UPCs through the GS1 and put stickers over your existing ones that you buy from us to go into those stores"
Quotes I'm seeing online are that to get your own UPC prefix number (which will give you 100,000 numbers you can use) it's about $900. Or you can buy from one of the many re-sellers for a few and like they say, if you get to the point of possibly going into WaMart, it's probably time to pony up and get your own numbers.
It is interesting, 2 sites reference the fact that the BigBoy retailers who won't accept reseller numbers are on the board of GS1. What a racket!