I've had a really tough time figuring out how to clamp my PCBs: my boards often look like the "bad PCB" here: http://www.flickr.com/photos/11461247@N02/5697373918/
I'm looking forward to testing out better clamping so my boards don't slide or vibrate so much: http://blog.holyscraphotsprings.com/2011/05/good-circuit-boards-require-good.html
Rockler Woodworking has a bunch of T-Track stuff, toggles and the like. All great stuff and well-made and probably much cheaper than a supply house for mills etc.
There was another place, Little Machine shop --they sell parts for all the cheapie mills and lathes. Harbor frieght, Grizzly and Central Mechanic. Might be some stuff there to help you as well.
I have not! I kludged some clamps using wood scraps, PCB scraps and masking tape, and haven’t upgraded. I’ve added dense double-sided tape to my shopping list. Thanks!