I had expected that such a conversion table could be downloaded from one of the Unicode sites in the Web, but if it is too difficult to find, it can be produced in your case without too much difficulty. Since you want to map iso-8859-1, the only interesting characters for the conversion table are those with an encoding between 140 (=128+32) and 255, so as a first step, you write a simple program which produces a file of bytes with values 140, 141, ..., 255.

In a next step, you use a text editor which can convert to and from UTF8. Since you are working with japanese characters, you likely have such an editor anyway. Otherwise there are plenty of free ones for the usual operating systems. On Windows, for instance, I use the Unicode Version of Michael Zacharov's EC Editor (http://www.econtrol.ru/. I think jEdit (http://www.jedit.org/), which is available for Windows, Unix and MacOS, would do as well. Using such an editor, you load (or paste) your byte string, and save it as UTF8. Using a Hex-Editor, you can see the encoding of these characters.