How to investigate what restaurants a particular supplier sells to?

Factual Questions
1

In this specific case, I want to find out if Darigold supplies any big restaurant chains with money and therefore the power to pressure Darigold into cleaning up their act (apparently some pretty egregious mistreatment of dairy cattle). But it would be great to know how to do it, period.

I was thinking of how McDonald’s successfully pressured pork producers to change their inhumane practices by making it a policy to only buy from pork producers that operate according to specific humane guidelines.

I got to googlin’ and got exactly nowhere. I don’t know if it was the failure of my queries or if this sort of information is just not very discoverable?

2

Givin’ it a little bump now that most folks are awake. I am really stuck and I have a lot of faith in Dopers to have answers that can’t be easily found elsewhere…

3

You could just ask them.

4

Is this something that a private investigator could find out? Staking out warehouses and restaurants, recording truck license plate numbers, etc. Might be expensive, but it sounds doable.

5

McDonalds for sure.

http://www.progressivedairy.com/index.php?option=com_content&view=article&id=8467:darigold-named-one-of-mcdonalds-2012-sustainable-suppliers&catid=36:industry-news&Itemid=62

Seems employees there are not too happy either

6

In general, this is difficult.
For nearly every business, the list of their customers is a very valuable resource, and tightly controlled.