I've used a good repair and alterations shop in Kobe on Center Street (the arcade south of Sannomiya station). It's in the basement under the Junkudo bookstore, next to the Saezeriya. On the same basement floor is a good condom and sex-toys shop, which is a plus. Around the corner on the street level is a very old bespoke suit shop. I can't remember the name, sorry, but they're quite friendly and I think you'll enjoy the shop.