Have you tried forbes.com?
If you prefer a Japanese source, this is nikkei.co.jp's list for the fiscal year ended in March 2008. http://markets.nikkei.co.jp/ranking/keiei/uriage.aspx
*Note that Japanese accounting rules are different from those generally accepted in the west; for example, trading companies (Mitsubishi corp, Sumitomo corp, Marubeni, Itochu, Mitsui Bussan, etc), which look huge in the list below, are actually about 1/4 of their size according to U.S. GAAP
Million yen
1 Toyota 26,289,240
2 Mitsubishi Corp 23,103,043
3 Mitsui Bussan 17,009,056
4 Itochu 12,387,908
5 Honda 12,002,834
6 Sumitomo Corp 11,484,585
7 Hitachi 11,226,735
8 Nissan 10,824,238
9 NTT 10,680,891
10 Marubeni 10,631,616
11 Panasonic 9,068,928
12 Sony 8,871,414
13 Toshiba 7,668,076
14 Nippon Oil 7,523,990
15 Toyota Tsusho 7,000,352
16 JT 6,409,726
17 Sojitz 5,771,028
18 Seven & I 5,752,392
19 TEPCO 5,479,380
20 Fujitsu 5,330,865
21 Aeon 5,167,366
22 Nippon Steel 4,826,974
23 NTT DoCoMo 4,711,827
24 NEC 4,617,153
25 Canon 4,481,346
26 Nippon Mining HD 4,339,472
27 Mitsubishi Electric 4,049,818
28 Denso 4,025,076
29 Idemitsu Kosan 3,864,263
30 KDDI 3,596,284
Find the rest at http://markets.nikkei.co.jp/ranking/keiei/uriage.aspx If you use the google translator you'll be able to read the companies names in western characters. Let me know if you have any question.