Any modern place (like Kitamura) is a digital minilab. They use machines like the Fuji Frontier that scan your film and then print it. Any place like this can easily put white borders on your film. Ask for borders and if you're using digital (which is a different aspect ratio than 4x6) as for "fill-in," which will give you borders and won't crop your image at all. If you manipulate your images on the computer and get them exactly how you want them, ask for "no corrections" and their machines won't screw it up. The Frontier is a very capable beast- I use it stateside on Fuji Crystal Archive for all my photos.
I used to use Kitamura for slides (they set it to Kodak/Fuji) and for prints from slides (about 100yen/4x6, decent quality).
I used Marmo in Irinaka, Nagoya for all my color negative needs. They have a tremendous selection of paper and are reasonable. It's run by a pro photographer and his buddy who dresses in US camo gear and they blast rap out of the shop. Cool cats. I used to develop and get 4x6 singles of my rolls on Kodak Royal paper for about 1200 yen, which isn't bad. Cheaper Agfa paper is closer to 800 yen.