Doubt if anyone here has a line on something like that. But, if you 'cast a line' out to go 'fishing' for a complete NOS system, I'm sure that someone will show up with one...at a very hefty price
Then you need to be very suspicious of their "find"....
P.S. No "complete" NOS 3x2 carb systems, including intake manifolds were ever produced, AFAIK. The 3 carbs may have been package together...but I doubt it. Doubtful that they were put together with a manifold as a single assembly group sold by GM as a [grouped] spare part.
Location: Graceland in a Not Correctly Restored Stingray
I'd step back and consider how valuable 3x2 intakes have gotten, and are likely to become in future, before doing anything to it which can't be undone. If you really "need" NOS, why not put the trips up for safe keeping and intstall a different carb/intake setup? JMO