Ajisen is a famous shop with 300 branches in 10 or 11 countries including Japan, China, the US (California), and Canada. They also have an online shopping site but I have not used it. The shop that I have tried in Tokyo (believe it or not but there are only two branches in Tokyo) is in Nishi Ikebukero, at the end of a long path, off the beaten path, going dirctly west from the station. This very informal shop closed at 8 PM on a Thursday, a bit suprising but maybe not really, given the fact that there was virtually no one in there at 7 PM, which is also a bit odd. I had the special paiku ramen, this is a special cut of pork similar to kakuni buta. The broth was good but a little "thin" in taste. The paiku meat was the best part. The taste was Kumamoto ramen style, with garlic oil, similar to Ramen Tai or Keika Ramen. Slightly different from Keika, for example, was the large amount of sliced negi onions in the bowl.
Shop home page
Gourmet Navi page
Diddlefinger Map (English labels)