There's no point in specifically learning higher AR(and especially not AR9).
Reading higher AR is linked to your eyes and the way your brain perceives and uses the information given by your eyes. The quality and speed of that process will get better if you play anything and mostly the highest common AR you're comfortable on - which is most likely AR8 for you.
Some day it will just make click in your brain and AR9 feels natural, no need to force it through specific AR9 practice.
That being said, you can search for maps with AR between 8 and 9 by utilizing the external site
http://osusearch.com and setting an AR-limit there(for example 8.1-8.7) to find maps that bring you closer to AR9 without playing AR9 itself.