On http://ftp.cc.monash.edu.au/pub/nihongo/00INDEX.html, you can find a list of 350'000 proper Japanese names (surnames, familiy names, names of places, etc) with Kanji and Romanji spelling (search for enamdict). Usagi is in there (interestingly enough as a female surname - at second thought "Bunny" is also female
... ahem) and Miyamoto returns 11 results including:宮本武蔵: みやもとむさし Miyamoto Musashi (1584-1645) (h);
Sakai returns 49 results, 8 classified as "person name" which seems to be the family name:
1) 栄居: さかい Sakai (u);
2) 区: さかい Sakai (u);
3) 佐貝: さかい Sakai (u);
4) 佐甲斐: さかい Sakai (u);
5) 佐飼: さかい Sakai (u);
6) 左貝: さかい Sakai (u);
7) 坂合: さかい Sakai (u);
8 ) 堺井: さかい Sakai (u);
Which one is correct for you, Stan?
Stan gives: スタン (u) Stan;
This page also contains software for various systems to use these files.
Hope this helps,