The switch is actually a combination primer push down function and a rotating on-off switch. It is a plastic rod, with a spring and a small metal blade on the bottom. The spring retains the metal blade at the bottom, when you put the shroud on, and the metal blade at the bottom performs an ignition shorting function when rotated. It shorts out the coil, thus stopping the engine. You should not be able to pull this rod up out of the shroud, unless your shroud is so worn that the hole is wallowed out. If so, you can perhaps use a washer under the shroud to keep the switch from coming up.
The parts are still available from the Toro/Lawnboy Store:
606865 Primer Bar
604248 Spring
604249 Blade
678414 Lawn Boy Carburetor Primer Assy Kit Lawnboy Toro Wheel Horse | eBay
Parts and Diagrams for Lawn Boy 7217, Lawnmower, 1967 (SN 700000001-799999999)
Above is the kit for this, also see diagram items number 36-40 for another view of the primer kit.
Also Stens has the same kit #525311