Quadrajet 4MV Hot Idle Compensator
 

69 Pace Car with 350/manual/AC. I have been running the car with the carb it came with - a Holley 4 barrel. My son got me an original correct numbers matching Quadrajet 4MV and he rebuilt it.

It is missing the hot idle compensator components. Where can I buy these parts? GM dealer?

Not all Quadrajets had the compensator, even though it would have the boss machined into the body, but not drilled through.
But if you're not building a down to the last correct nut & bolt restoration, you can block off the opening on the carb.
Have you tried looking on ebay?
And just to make sure, you're referring to the hot idle vent in the back of the carb, and not the idle vent valve on the top cover.