I haven't found a shapefile yet but, if you are OK with json files, you can download it
here (where it says Citi Bike stations status feed (json)). That json file gives you the lat/long coordinates of each station that you could add to a map.
If you've never used json and prefer a flat file (excel of csv)
this website will convert the json to an excel file.
Not use if that what you needed but I hope it helps.