I'm a fairly regular player at their monthly walkon games, which is on the second Sunday of the month.
It's a mixed group, normally between 20-40 players, all sorts of gear and varying levels of experience.
The games are played across most of Campaign's fields so there's a good mix of woodland and themed fields. We normally end off the day with a bash on the Sup'Air field.
You have to have all your own gear, they provide air or CO2 , paint, and a cooked lunch.
You might try
www.talkpaintball.com as that's the main site for co-ordinating Campaign games.