We use them quite a bit at work. I had one, but it ended up disappearing. Snap on rapes you about 30 to 40 bucks a piece for one, so did not want to buy one from them.
I needed one when I broke an intake bolt and the drill bit would just wander when I was trying to drill it out. This town sucks for getting anything you need. Looked all over at harbor freight, but did not see any. Seen Sears had a pack of 3 for 30 bucks, but they were very small, smaller then the ones I normally use. Ended up buying one off ebay, for 7 bucks with free shipping,like I have to order off the computer for most of the stuff I need, never being able to find anything in town. Bought from this ebay seller. http://shop.ebay.com/merchant/qualit...Q_fromZQQ_ipgZ
A guy at work said he got his one year when there was a guy selling them for 5 bucks a piece at iola, a big car show every year in this area. Maybe if there is a larger car show in your area with a lot of venders, you could find some there as well.