Contact a serious GC distributor like SVM and ask about discounts. If you buy say $50,000 worth at a time, all from the same merchant and in the same denomination, you could probably get somewhere around 2-3% off, 5% if you hit the right merchant at the right time of year. Otherwise your solution is pretty much to trawl eBay and other marketplaces for whatever you can get (and you can get them for pretty deep discounts, but your posts seem to imply you're looking for a steady and specific supply, which simply does not exist in any legit form without bulk buying.)