Short Activity in PNV, page-4218

Nearly... though what you describe is pretty close to what institutional cash desks do... fund manager calls and indicates an interest in a block size quantity of stock. The broker makes a few calls to people who she thinks might be able to take the other side, including potentially her own bank's balance sheet, and if successful comes back to the fund manager with an offer. They might have a couple of iterations to set the price and the deal gets printed to the market as a block crossing. Commission is normally the "usual amount" - that is, some managers pay more or less than others for cash-desk transactions, but variations tends to be small. Differences in the stock price for the deal make much more of a difference to the total value of the trade.

And that's how an off-market crossing is born.