I've heard that JBJ Cycles in Santa Ana might mount one for you, but you'd have to give them a call to confirm. If so, they might suggest a place where you could buy one.
If you're mobile and feel like a half hour ride, c'mon down to San Clemente and and visit S.C. Rider Supply (http://www.scridersupply.com/). They're great folks and they mounted my CT for me. There is a CT shop right next store to them who could probably sell you a tire, too. Or, there's a Wally World here in town (about 3-4 miles away) who might be able to take care of you.