Its not as impossible as it seems at all. All you need is the IP records that go with the sales. Thats it. The pattern becomes very very easy to see REAL fast. Blindingly so. So fast that a decent coder could look at what the DTCC has and literally write a program to correlate the data. VERY easy to do. VERY easy to parse that data as they call it. Hard to implement as DTCC is utterly locked down and reports to literally NO ONE. There is ZERO over-site of them currently. THAT has got to be addressed.
You still didn't address the "street name" problem.
I'm a bank, or I'm a brokerage house.
I hold half a million shares of Stock X for any given number of owners.
What I do, instead of registering the entry at DTC for each of these owners, is to have a single entry under a street name which my own internal accounting system allocates among the various accounts to which pieces of this big block of stock gets allocated.
Methinks what you really want is either the stock exchange records or the records of the trading firm.