Mark, need not worry. there are plenty of runs available!
http://www.4wdlow.com/runs.htm
They're abunch of great guys that do runs once a month. There are also other groups so just check around
the socal ttora guys do a run once a month too btw.
Depending on where you live (i.e. SD, LA, OC) there are plenty of socal folks that are willing to do a run w/ ya!
Btw, there will be another Pismo run in August time frame. Also at the sametime, we're working on a Big Bear run as well (weekender)
On a side note, most all groups will accomodate for your abilities but you should make sure and confirm it w/ the trip organizer so they can pick the trails accordingly when you arrive.
So what excatly is a trail run? I have a 2wd and have never driven off road before, can I go to something like this? The 4r is all stock, I don't know how well it would handle a serious trail run.