It can be found on a desk in a second-floor room in the far northeast corner of Puesta del Sol North, accessible only through a broken hole in the wall above a courtyard filled with the Cloud (the Cloud may have been cleared if the Courier has reactivated Puesta del Sol's ventilation systems at the Puesta del Sol switching station already).
Starting from the door to the switching station, turn south and jump on the left hand pipe. From its end, jump onto the overlapping roof and follow it east, past the courtyard with a dead tree and a hole in the right hand wall. Continue eastward on the roofs until reaching the cloud-filled courtyard, with the hole located right up ahead. Switch to the right hand roof while avoiding the two bear traps, and enter the hole to find the note on the desk.
Liquor shipment finally came in today - didn't realize working here would be like working in a dry state. Just need to keep it out of sight of security and Sinclair, and ought to take the edge off the day, keep it stashed in the back.