Well, RAM sold well under market prices was likely recovered from an auction of stolen items or bought from a company that did a major upgrade then sold off the removed pieces. The discounts you get on a highly competitive product like DRAM isn't going to vary a huge amount when bought in bulk lots because the mark-up is so low to start with.
You never see RAM at 50% off the market price because 1) there's not that much markup to allow it to be sold so cheaply 2) Anyone would be a fool to sell it so low when they could parcel it out in smaller lots and make so much more.
And by market price I mean a company that sells a LOT of retail RAM, like Newegg. The reason you might buy at Newegg over Joe's Computer in your town is because they already have the best prices - with no support of course.
Here's a company that advertises Wholesale Quotes - but not sure how much cheaper that is than a company that deals in a LOT of RAM like NewEgg:
http://www.memorysuppliers.com/contactus.html
However, many manufacturers sell DRAM directly, including Kingston. Might as well start with them.
http://shop.kingston.com/contact/default.asp
Remember to get at least one retail pair to fully test the product you decide on before ordering 200 of them. You'll not find generous return policies at wholesale prices.
(I worked in the wholesale and retail computer business for over 10 years before starting my own company. One of the fun things about the RAM market in the 80s was the wild fluctuation in wholesale and retail prices. A single RAM chip that cost $2 one day might cost $8 in a couple of weeks. Normally, even today, the rule is you never buy a large stock of RAM. Unless you're really sure it's gonna rise heavily soon. By taking some risks in buying a large stock, I would often be making more selling the RAM in a system than the entire rest of the sale. Of course, like any market trading, one mistake and all your profits go poof!! The trade papers back then would report every calamity that befell RAM factories in the Far East - a big fire there and an earthquake somewhere else would mean profits could be made.)