They can be bought in 鐵道模型 shops.
If in Japan, you can buy in Sakuraya shops - price are very good.
If in HK, you can buy in some 鐵道模型 shops. If in Wanchai, you can also buy in "Red-fat", price is around 7 算 after the so-called discount.
Another way is to buy the buidling from 玩食. e.g. Tomytec 街並
http://www.tomytec.co.jp/hobby/machi/index.html
Below are my works in progress...
More pics:
http://www.toysdaily.com/discuz/viewthread.php?tid=15285