Sure enough, you can get it on Day 4 if you haven't purchased it already. I can see why I missed that. It's available sooner to the brigand and rogue. The brigand gets it handed to him on Day 2 (after certain events), while the rogue still has to buy it, but can do so on Day 2 as well. As a sorcerer, I had to wait until Day 3 before I could buy it, and by then it wouldn't have occurred to me to wait until Day 4 for someone to give it to me.