You can probably find a few folks (and a bit of interesting discussion) at the Working Pit Bull Forum. It's linked on the main page of the Working Pit Bull Terrier Club of America.
www.wpbtca.com
You can probably ask around on that board about lines and whatnot . . . and Ron, Leri, Howard, and others do post there.
There are some nice dogs working out there right now, but I think half the battle is finding the right dog; the other half is finding someone who knows how to work a pit bull in protection sports.
I have a dog that I'm working in schutzhund right now, he came from god only knows where. Landed in my lap after a series of failed homes. The dog works well in protection and can take a lot of pressure . . . but he's kind of a crappy obedience dog. We actually failed our SCH I last month because it was hot as hell and he just wasn't in the mood. He was really flat, really miserable, and really stressed . . . so we passed our protection and our tracking, but frigging obedience, which should be the easiest thing, was a train wreck! :roll:
BTW, don't know where you're from, but the WPBTCA is having it's 2009 nationals in Flint, Mich. this year. If that's anywhere convenient for you, you could come out and meet some of the working pit bull folks and see some solid working pit bulls in action!