I hear you. I've struggled with this problem on 3 different 440 HP cars in the last 10 years. Are you missing everything? If so, keep the following in mind:
There are maybe 25 total parts in the setup. The correctly functioning 3-segment linkage came on 1968-71 440 cars, both B and E bodies. But 2-3 of the parts look different in 1970-71. The difference between the 440-4 and 440-6 setups is at most 2-3 components. Even a full 383 setup will get you most of the parts, but rod P8 is longer on the 440 and the 383 rod can be extended to work. So, if you find a full 440-4 setup, buy it, because it will give you most of the parts. This one on epay looks pretty good for $500. I've looked it over, and it looks correct for 1970. $500 is about the going rate for an OEM setup.
440 4BBL 727 KICK DOWN LINKAGE 68-71 CHARGER GTX 70 71 CUDA CHALLENGER R/T MOPAR | eBay
A diagram from the Dealer Parts Book for reference.