I wonder if you could use the vex rack and pinion parts? you'd have to make a support thingy for it, and the stuff that it's made to bolt to is all steel (or aluminum), but you might be able to make something from plastic.
http://www.vexrobotics.com/vex-robot...gear-kit.shtml
also Lego comes to mind, I think they have some short stroke rack and pinion setups in some of the car sets? My son Steve might know, he still plays with Legos (and he's in college now)