Actually Chris, they've bought large lots from secondary sources, ie dealers or other private sellers, coin shows, auctions, estate sales, some from the mint directly but not a lot. I know a guy in Albion, NY that buys large lots of different moderns, more UNC, than PR, and sends them in for grading. Out of 20 coins he submits, he gets a MS-70 graded return on about 1/4. He turns around and lists them on craigslist for 3.5x FMV.