Hi PassionPlay,
I would suggest that you try the local newspapers. There are a number of papers that you could try. The Methyr Express generally has pretty good coverage of the valleys and different editions covering different areas. I have done a look up for someone else regarding Caerphilly Council and found lots of references to Council Meetings, a general profile from a series called "Men at the Wheel" and a specific council event that they had details of.
There is the South Wales Echo, which I have only viewed a couple of times for specific family events. I do not know what the coverage would be like.
There is the Caerphilly Journal. This was published in Pontypridd and seemed to be biaised towards that area, (even although it is a Caerphilly paper).
These papers are available at local history libraries, although availability and editions vary. I have used Methyr Tydfil, Tredegar and Bargoed in the past to access the newspapers.
As the papers are not indexed, it is helpful to have a specific event or a reasonable date to research, otherwise it is like looking for a needle in a haystack.
If you are not local, I am hoping to go to the library tomorrow (Wednesday) and I can have a quick look, if you can give me some details of a specific date.
There may be books available on the history of local mines / unions/ villages, but i don't know of anything specific.
Ore Dragon