Where to get ACM references for MS Word?
Managing references can be a tedious task, especially at the proof-reading step of a paper and the usage of software that keeps track of your paper/references library (e.g. EndNote or BiBDesk) can be strongly recommended. 

With such software you can have all your references in your paper formated accordingly and automatically to the style that either you choose or the conference/journal wants. 

In MS Word there is an option where you can integrate EndNote, insert references and have an automated formating and arrangement/re-arrangement. Integration is done automatically for EndNote and MS Word, just when you install both of software. 

ACM style quide can be found here.