Only one that occurs to me is rather simple map by Cheung Chau Bookstore, about opposite the post office (in big govt services building a little south of the ferry pier). Can’t remember how many streets it shows, but does only cost a few dollars.
Online, you could have a look at, say, centamap:
http://www.centamap.com/cent/index.htm [just checked, and not working well for me right now]
http://www.ypmap.com/ – which is working just now.
And perhaps check products by govt Survey and Mapping Office: