Tomioka Hachimangu Shrine hold flea markets twice a month in my neighborhood.
There are over 100 shops, and it’s impossible to look at them all at leisure in an hour or less.
There are also several wristwatch shops.
There are several stores that carry Seiko Vintage such as the Grand Seiko, King Seiko ...etc.
You might hesitate to buy one since they are a bit expensive, but its also fun just to window shop.
The most interesting part is the junk box aside the store.
Most of the watches are broken, but there are some functional watches as well if you search long and hard.
My wife found this watch for 1000 yen(about 9US$). It started working when we changed out the batteries.
You can find the schedule for flea markets held in Tokyo on this site.
Why don’t come to Tokyo and check one out if there are any scheduled?