The pump kits are out of production and have been for some time. The only way to get one now is to purchase a complete pump mag or to buy the parts from someone parting their pump mag. Brad Nestle at PBMaxx was making some kits a few months back, but they are not out of business and he isn't making any kits. You can always get someone to custom make one for you, but they will usually need a kit to look off of to get the measurements.
Also, you will need to make sure your body and rail are milled with a pump slot so you can put a pump kit on there. Honestly, the pump kit will cost about the same or more than your 68 Classic. Your best bet is to purchase a complete pump mag.
"How would you like one across your lip?" - Fred G. Sanford My Gallery History:
Line SI Bushmaster; PMI-3; VMX; '97 Autococker; KP-3; Enforcer 2(possible SWARM); Spyder Sonix; Monteneel Z-1; PGP 2K; BBT Typhoon; 2k1 SP Impulse; SP MiniMag; another PMI-3; VM-Magnum; Blazer #153; Pump MiniMag; Thrasher ULE Emag; Cool Camo Micromag; '94-'95(?) Evolution Minicocker; '95 Evolution Autococker; Blazer #710; CNC X-Mag; Gold Rush Micromag; Jungle Sunset Micromag; Wild Tiger Micromag