Hi Bsollish. I did an internet search and found a few options that hopefully work out.
It looks like Orient Auto Parts & Recycling in Gresham, Oregon has one. Their number is 503-663-1909. Its from a 1977 model but the latch is likely the same. Someone may be able to confirm it for you. Here is the inventory listing.
Chevy 10 Van G10 SLIDER DR Inventory # 181U $35
Let me know if this works.
Also, the little plastic lock rod clips that get brittle inside the door can be found through Dorman part #75454. The striker can be also found as a Dorman replacement part #38428 through most auto parts stores and online if you need those.