The power points section on p. 278f confirms your assumption. Of course that means mystic adepts either buy the power points at character creation or loose the opportunity to do so permanently. However there are a few ways of gaining new adept powers after character creation that do not require buying new power points:
qi foci (core rules p. 319) can give you additional powers (or increase existing ones), but you'll risk focus addiction if you go overboard
getting a mentor spirit (and choosing the adept power(s) as mystic adept) (core rules p. 320ff)
blood magic adepts can temporaryly steal powers from other adepts with the power bleed meta magic (Streetgrimoire p. 90). But the drawback is that most people will try to kill them, if they recognize they're a blood mage, or at least organize a manhunt...
And the GM may not allow it - or just die laughing if you try to convince him/her to allow it (they do this in the missions faq - seriously)
Following a way (Streetgrimoire p. 176ff) can reduce the cost of adept powers, which allows you to buy new ones; but the number of points you can reduce the costs sum up to at most MAG/4
The infusion meta magic (Streetgrimoire p. 156) allows you to temporaryly increase the power of one of your adept powers, but that has some nasty side effects
the qi sculpt meta magic (Streetgrimoire p. 156) allows you to "transfer power points" between 2 of your powers. (Also nasty side effects)