Perhaps you're really into antiques, and those cool, unique one off finds that you can't just walk into a shop and purchase.
Shrine sales might be something you're interested in, then!
My mother in law was the person who introduced me to the idea of shrine sales. She has spent a great deal of time in Japan, since my father in law's career has required their family to live here for several year stints at a time. Her house is beautifully decorated with all manner of Japanese furniture and ornaments, and naturally I was curious about where she was finding all these magical things!
Basically, shrine sales are like antique fairs for Japanese wares (unintentional rhyme, there!) which are held on the grounds of a temple or shrine. Depending on the venue itself, you may have only a handful of vendors, or you may have 100+.
This particular link does quite a good job of summarizing what shrine sales are on each month in the Tokyo area, as well as including the nearest train station if you're headed to a particular one.
One of the best shrine sales I've been to in Tokyo was one out in the suburb of Machida - this was one where there were probably in excess of 100 vendors, so it made for a great day of treasure hunting. Kawagoe also has a really fun one, and that's a town worth looking around anyway, since it's still set up like an old Edo village - definitely worth a day trip to explore more than just the shrine sale if you do go!
These pictures were ones that I took from one of my first ever shrine sales. In the first picture below, do you see that beautifully decorated set of 5 brightly colored sake cups? I loved them, and really wanted to get them - until we found out they were the equivalent of $350 US dollars as they were from the Kamakura era (sometime from 1185–1333)...so I guess you could say I had expensive tastes for a first timer! Oh well, the picture lets them live on in my memory!
And these were my actual purchases from my first ever shrine sale! I guess you could say I was gravitating towards green things - I got that adorable kokeshi, some shisa dogs (these originate from Okinawa and they're seen as a protective type thing for your house - you see them a lot if you're visiting Okinawa!), another Shisa dog that was on it's own that we have dubbed our "chopstick guardian" (he sits on our kitchen bench with all of our chopsticks in it!) and that pretty vase.