Kappa-bashi is located near Asakusa in Tokyo. This shopping street has many stores which treat tableware or equipments for restaurant. I found 3 stores which treat food sample.
Kappabashi Dougu Street: http://www.kappabashi.or.jp/en/index.html
Niimi tableware store
Probably this store doesn't treat sample of foods. But I introduce this store because it stands out in Kappa-bashi. This is a tableware store and the big figure on the top of this building is the store's president.
Inside of this store is very bright. This store has web site and is selling sample of foods on the internet.
Web: http://homepage3.nifty.com/310sample (for Japanese only)
Standard and small size samples are selled in this store. However it's expensive although it's size is small. The shopgirl teaches us many things about sample of foods.
Web: http://www.maiduru.co.jp (for Japanese only)
You may watch this store because some samples are offered at a special price. I could buy samples of Japanese cake at 500 yen. In the web site of this store, you can see many photos of samples.
Web: http://www.office-web.jp/tokyobiken/ (for Japanese only)