I would like to address this topic again
it is 2016 ( actually, we started 2017 by now:), and I am 6 years smarter.
One sentence rings in my years every time I remember this topic, someone said that people who have their channels to get large amounts of LEGO bricks keep it for themselves, or keep it quiet
When I started this topic, I was looking for 10.000 1x2 bricks. Today, I think I have 500.000 1x2 bricks (I still think they are greatest for building large things), and I also bought a ton of other bricks, with not so much money invested.
I would like to share my experience:
Bricklink: use wanted list, and switch from "larges quantity" to "lowest price". Use "min parts required" to root sellers that don't have as much as you need - don't buy when you need, buy when there is a chance for a great deal. Ask for discounts. Pay special notice on massive sellers who have flat shipping (like German shop bricksy (I am not affiliated in any way), they have a ton of bricks and 3 flat shipping for Germany, 6 for Europe and 10 for world - that means how ever much you buy, the shipping charge is the same. I once bough 35 kg of bricks, paid 6e for shipping.
PaB: great for small parts, not so great for large. If PaB is on weight, great only for bamboo leaves, nothing else, as far as I know. Get friendly with manager or some other employee, ask to be notified if the brick you like arrives. Follow brickbuildr or similar sites
Lugbulk: every Recognized Lego User Group (rLUG) has opportunity to buy, once per year, loose bricks in large quantities with great discounts directly from Lego Company. You have to pay for shipping and VAT from your country, and that is that. There are some rules, ask your local rlug representative for additional info. Prices are privilege information, only the one who join lugbulk program get them. Trust me, they are very good, especially as they are not depending on color, but amount of plastic used - this meaning 1x2 in white and 1x2 in sand green is probably going to be the same price. Like I said, there are some rules, like no reselling policy, and your rlug should know them all.
You can find lugbulk rules and guidelines here: link
If you are not sure if there is a rlug in your area, check this map here
Resellers, blackselers: after some time in AFL world you get to know a guy who knows a guy. Boxes fall of a truck, resellers get gazillion bricks from shady stocks, someone is selling their whole collections, someone needs money asap and has bricks to sell, etc - keep your eyes and years open. Few years ago, I met a guy in Hungary who had his house full of bags with Lego bricks. He had a bench on the vegetable market where he sells LEGO bricks on grams. And he was not the only one. If you get friendly with someone from AFOL community, ask for contacts for re-sellers and black-sellers. I don't know if it is illegal, but when I shop over bricklink I never ask for paper on where did the bricks came from
Conventions: on massive conventions (like Fan Weekend) there are sellers who sell with great prices. You can also make good contacts
Project support: again, RLUG members can be part of the Project support that handles loose bricks as support. Please ask your rlug representative for suggestions