Well, they're listed as promo cards, but shouldn't promotional material actually be something given away to promote interest in a game? This is really just a mini-expansion. Or has there been any information about these potentially being available at, say, GenCon or Origins (or even available to buy anywhere than through BGG)?
The Envoy was a giveaway at the Vienna game festival last year.
It has been hinted that the black market will be a giveaway in the german Spielbox magazine.
The publishers decided to make them available to everybody, and make an additional distribution through BGG.