I'm also a newbie but from my understanding:
If you're looking on the Gal's DB any girl that has (Have Special Service) at the end of their review will most likely do Anal.
More milf type WG will do this for extra money.
If you're looking for younger women i would suppose you would have to be a regular(Don't quote me on this one)
Here is an example of a sure Anal experience
http://sex141.com/en/475-tsim-sha-tsui-141-walk-up-sa-sa.html