For commercial stuff (advertising industry), portfolio visits and relevant marketing is essential. You’d need to find out who the ad agencies, art directors etc are, make contact with them, set up meetings and show your portfolio. Mandarin would probably be essential, or at least very helpful. Shooting commercially, you’d need a proper registered business or open work permit.
For editorial (magazines etc), you can’t really make a living just on the local market unless you take the jack-of-all-trades approach, which is rarely a good idea. As such, you’d be marketing your work throughout the region - Taipei, HK, Bangkok, Singapore and possibly Jakarta and Shanghai. This is where the rep office approach would work best, and Mandarin wouldn’t be so necessary (but would still be helpful).