The indications began when the show's co-creators, Dan Harmon and Justin Roiland, posted pictures on Twitter of a half-gallon bottle of the coveted sauce that McDonald's had sent to them.
Following that, McDonald's gave away three other bottles via a Periscope livestream that was broadcasted through Twitter. The three lucky individuals that received the bottles of sauce were just announced and received messages in their DMs, as the livestream indicated.
While McDonald's claims that this is all of the sauce they have for now, they've left the door open for more to possibly arrive in the future. A statement given to Business Insider claims that "when our customers speak, we listen," giving us hope that more Szechuan sauce may arrive soon.
Considering that a live-action Mulan movie is coming next year and the last time Szechuan sauce was available at McDonald's was when the original film came out, there's a good chance we'll see some in restaurants by then.
For now, if you don't happen to know one of the lucky winners, you can do your best to recreate the sauce following this recipe.