Sorry , I don't have anything I can share. 

It is a gathering of policies we already have to review. During this review there will likely be items that haven't been documented. 

The business rules will be to make sure they are documented somewhere but the main focus will be to use them for some other projects that will be occuring at the same time. 

Can you suggest a methodology and/or any good books on this ?

Hi:

Documenting  business rules is detailed work.   If your system is complex, a majior challenge is to effectively decompose the system to arrive at small processes that are of approx equal size and that are loosely coupled and highly cohesive.   Without doing this decomposition first - before moving on to the detailed rules documentation - your rules will be an intertwined mess of spagetti that can be impossible to organize.

Effective decomposition of larger scale systems is only offered through data flow diagrams.  

Tony Markatos

 Tony,

Using decomposition or any form or process modeling is absolutely NOT needed for business rules discovery, you want to separate your rules from process and system., and avoid entangling them in process and any automation of that process. 

Start with business vocabulary, use it as a basis of a Fact Model, and build your rules up from there, using policy statements, relevant regulations, and other sources.

Then see where your processes need guidance and decisions based on rules, and cross-reference the two, but do not embed rules in process.