Hi Donna,
There are TC's & XP's out there. Being in Ca doesn't help with all their restrictions on guns so finding one in Ca may be a bit of a challenge. There is a IHMSA web site you might find interesting The link is
http://www.ihmsa.org/ There is a match schedule there showing the clubs that shoot. They are listed with contacts on the web page:
HAT CREEK R&P CLUB, BURNEY
SIERRA PISTOL CLUB, FRESNO
INLAND SILHOUETTE CLUB, REDLANDS
L A S C, LOS ANGELES
OJAI VALLEY GUN CLUB, OJAI
As for guns I personally like the 6.5mm. I have a Rampro STP in 6.5BR as well as a 10" TC in 6.5TCU. The 7mm are also very popular. I also have a couple of xp's in 7BR and TC's 14" and 10" in 7TCU. The 6mm work well for 1/2 scale. They work for BigBore if you use the heavy bullets and rams are set proper. May ring a few with the 6mm if the club has tough rams. If I were to pick one caliber for unlimited it would be in 6.5BR. The TC would probably be a little easier to come by than an XP but you cannot put a 6.5BR in a Contender. I am also a bullet swager in which I swage for 22, 6.5mm & 7mm. Got into it when I bought the Rampro in 6.5BR. It has a break and tight neck chamber which means jacketed bullets are a must so for this gun I had to forgo the cast bullets and start using jacketed. Hope this helps.
Bret