A good starting point might well be the existing leaders that currently don't have a pic either in your mod or from paradox (dates as currently shown in files):
Suzuki Kantaro (1905-1929)
Sato Tetsutaro (1907-1922)
Tachibana Koichiro (1909-1922)
you could also consider looking into some of the leaders from the VIP file for which pics might be found:
Tokugawa Yoshinobu (1857-1869) - last Shogun
Okubo Toshimichi (1860-1878) - Boshin war, Satsuma forces, General under the Meiji government
Katsura Taro (1866-1913, although i'm sure that VIP has extended his service way past, he was already retired and prime minister by 1901)
i've loaded all the japanese leaders from VIP into my easy unrar of your mod, for when MP games use it.
You could also consider some of these fellows...
Army Commmanders during the Russo-Japanese War:
Kuroki Tamemoto (1871-1909)
http://en.wikipedia.org/wiki/Kuroki_Tamemoto
Oku Yasukata (1871-1911)
http://en.wikipedia.org/wiki/Yasukata_Oku
Nozu Michitsura (1871-1908)
http://en.wikipedia.org/wiki/Nozu_Michitsura
Generals:
Saigō Tsugumichi (brother of Saigo Takamori, commanded during the Boshin war and the Taiwan expedition, was part of group sent to study European tactics and technology)
http://en.wikipedia.org/wiki/Saigō_Tsugumichi
Kuroda Kiyotaka (early figure - Boshin war, opening of Korea, commanded under Yamagata Aritomo during Satsuma Rebellion)
http://en.wikipedia.org/wiki/Kuroda_Kiyotaka
Shunroku Hata (an artillerist)
http://en.wikipedia.org/wiki/Shunroku_Hata
Yui Mitsue (general in 1907, important role in the Siberian intervention 1918)
http://en.wikipedia.org/wiki/Yui_Mitsue
Kawamura Kageaki (commanded Imperial Guards Division in Sino-Japanese war)
http://en.wikipedia.org/wiki/Kageaki_Kawamura
Yoshinori Shirakawa (various army commands in the 1920s until 1932, when he was killed leading an expeditionary army in Shanghai)
http://en.wikipedia.org/wiki/Yoshinori_Shirakawa
Senjūrō Hayashi (commanded the army in Korea during the period of the Mukden Incident)
http://en.wikipedia.org/wiki/Senjuro_Hayashi
Shigeru Honjō (commanded Kwangtung army during the invasion of Manchuria)
http://en.wikipedia.org/wiki/Shigeru_Honjo
Sadao Araki (one of the more colourful figures and strategists during the 1920s and 1930s, advocated mainland expansion, helped to plot the Mukden incident)
http://en.wikipedia.org/wiki/Sadao_Araki
Admirals:
Kawamura Sumiyoshi (important early figure in the IJN, naval academy figure, commanded during Taiwan expedition and Satsuma Rebellion)
http://en.wikipedia.org/wiki/Kawamura_Sumiyoshi
Uryu Sotokichi (1900-1927 - even a colour pic on wiki!)
http://en.wikipedia.org/wiki/Uryu_Sotokichi
Itoh Sukeyuki (commanded fleet during Sino-Japanese war)
http://en.wikipedia.org/wiki/Itoh_Sukeyuki
Dewa Shigetō (commanded a squadron during several sea battles in the Russo-Japanese war)
http://en.wikipedia.org/wiki/Shigeto_Dewa
Prince Takehito Arisugawa
http://en.wikipedia.org/wiki/Prince_Arisugawa_Takehito
and this familiar figure was already a rear admiral before the end of Revolutions:
http://en.wikipedia.org/wiki/Isoroku_Yamamoto
Take your pick, lots of interesting people to choose from!