All matters flapping have tended to be raised in this thread;
http://www.theracingforum.co.uk/forum/viewtopic.php?t=11838
Some of the protagonists on there may be able to tell you who calls at these meetings.
As regards the broader question, there are a few ways of getting into commentary. Approaching organisers of point-to-point meetings for a try-out, and / or sending tapes to providers of commentary services, would probably rate the better-known routes for Rules and point racing. I wouldn’t be too sure flapping meetings get to use any commentators from within those spheres, though.
gc
The patron saint of lower-grade fare. A gently critical friend of point-to-pointing. Kindness is a political act.