Go up that street by the Sunshine Cinema 2 and pass by the Sunshine City department store. Anyone ought to be able to point you in the right direction. Make a U-Turn and go back to Shinjuku. On the West side of the JR station, there across the main plaza you'll see Subaru HQ and its showrooms. Call ahead and find out what the schedules are.
Some places are closed midweek so that they can be open both days on weekends.
Usually falls on Tuesday or Wednesday. I highly recommend you call ahead of time to check if a. Most if not all are located in phone books there, or you can ask friendly sales staff at places like Super Autobacs. Keep your eyes peeled and you will see the same kind of craziness running through the Tokyo streets that I was priviledged enough to witness first hand last summer. A conversation knowledge of Japanese is not necessary to get by in Tokyo as most people are more than willing to try out their English - but it sure doesn't hurt.