So, it's the three tier system. They are actually selling it to a distributor, who is then selling to a retailer. They all have their own arrangements with someone, because that's how the gift shop works at all the distilleries.
Before the boom, barrels could be purchased pretty readily. From my understanding, Buffalo Trace wants you to work your way up. So buy a barrel of Buffalo Trace, then Weller Antique, then Eagle Rare, etc. But now everything is just bat sh1t crazy. More than likely, if that is a personal barrel, he knows someone fairly high up, or he's bought before. Barrel's of Blanton's don't happen easily. Although, it could be as simple as he was on a list and his name came up.
I read an article about Eagle Rare a few years back. Talked about the process of picking a barrel. At the end, they offered to send the barrel to Corazon Tequila to age a barrel for him, if he wanted to purchase. How cool is that, using the same barrel for both.