Titchfield Offroad Club (TORCH) is pretty close, depending which bit of the Forest you're in. We race pretty much every Sunday morning, and aim to have at least one 'all-day' event a month.
The club website is at
www.torchracing.org.uk, and has a map so you can find us. We're also on Facbook, see the link in my signture below. We'rea frienly bunch and would love to see you at ore track.