As the others have mentioned, Kappabashi is the mecca for plastic pickings.
For more background info, I recommend watching the 1985 film
Tokyo-Ga by Wim Wenders. It's fascinating and wonderful documentary on Tokyo and includes a tour of one of the replica food factories. FYI, he also tours a factory where they make the arcade-style pachinko machines.
You can also find convincing replicas in magnet or keychain form at souvenir shops. I picked up some amazing chicken and quail egg magnets at Tokyu Hands not long ago. Their real-unreal yolks consistently garner critical acclaim on my fridge. Now where's that bacon...?
Here are some recent findings at Haneda Airport.