I was looking up old maps of Pusan and upon looking at the University of Texas Perry-Castañeda Library Map Collection I found that their Korea collection had a new addition: Korea City Plans - U.S. Army Map Service, 1944-1946.
The map images in this collection include Seoul (which, along with Pyongyang, was already at that site) and a handful of ports now in South Korea (the Japanese names are in brackets): Kyongsong or Seoul (Keijo), Chinhae (Chinkai), Kunsan (Gunzan), Masan,Mokp'o (Moppo), Pusan (Fusan), and Yosu (Reisui). The bulk of the maps are actually of present-day North Korean cities, including those near Pyongyang (Heijo) - Chinnamp'o (present-day Nampo), Kyomip'o (Kenjiho) (Present-day Songrim), and Haeju (Kaishu) - as well as those on the east coast (in order from south to north): Wonsan (Genzan), Hamhung (Kanko), Hungnam (Konan), Najin (Rashin), Ch'ongjin (Seishin), and Unggi (Yuki) (Present-day Sonbong).
I wasn't sure where Kyomip'o or Unggi were, so some searching turned up the links above, as well as this photo of the Mitsubishi iron works in Kenjiho (Kyomip'o), which is south of Pyongyang on the Taedong River:
For other photos of some of the cities mapped above, go here for a folder (in a zip file) of colonial-era photos commenter Mika pointed out to me over a year ago (the download 'button' is at bottom left, you have to wait 20-some seconds).
There are photos of colonial Seoul (Keijo), Incheon (Jinsen), Busan (Fuzan), Gunsan (Gunzan), Daegu (Taikyu), Daejeon (Taiden), Pyongyang (Heijo), Sinuiju (Singisyu), Cheongjin (Seisin), Wonsan (Genzan), Hamheung (Kanko), and Nanan (Ranan). In all, there are about 330 photos in the 80mb zip file.