Good luck. I tried to organize a group buy for a very large home brew club, and unfortunately we couldn't get anyone to help us out.
I reached out to a lot of the guys on here that started some of the group buy threads, and most of them told me they had a hookup that made it possible for them. Either they worked at a brewery, or a store, or knew someone at one of the distributors.
I called and spoke to several of the sales reps for big home brew supply distributors in my area, and they all told me they don't sell directly to individuals or clubs any longer, and we'd need to go through a LHBS. I contacted all of my LHBS's, and the most any of them offered was a 10% discount, which was only 5% more than they're standard home brew club discount.
We chatted about it, and came to the conclusion that it makes sense. The distributors don't want to undercut their retailers, and the retailers only have so much of a markup and figure you're going to buy it anyway since you can't buy it directly.
In the end we just got that LHBS to extend that 10% discount full time to our club members, which was nice.