My two favorite locations for getting the lv. 10 and up abilities are Sai Kung C and Stamos NW. Both accessible by subway and both safe for those who are looking for the abilities in question... though you do have to watch out for Agents at both, of course.
There`s also a Martial Arts vendor next to the Subway entrance on Stamos Central and another one very close to one of the Hampton Green`s hardlines, also next to a subway entrance. Check these before coding any martial arts abilities from level 20-30.