I found on HP forum site the following advice:
The Laserjet 4M drivers (and many others) are actually available through the Windows Update process. Try the following: go to the Printers folder, select Add a Printer, select the appropriate port, then when the "Chose a Printer Model" dialog comes up select "Windows Update".
Unfortunately, there was one strange Windows feature or probably a bug... as it always happens with Windows. A first bug I discovered in Windows 7, which is actually much better than its predecessors.
When I tried to installed my LaserJet 4MPlus network printer on Win 7 64 bit by clicking Add Printer, as you described above, there was NO Windows Update button visible. Finally, I selected an incorrect printer model and installed that printer driver. After doing it, I right-clicked on a printer, chose Printer Properties => Advanced => New Driver and ... what a miracle: Windows Update button suddenly appeared!
If you ask me how did I find this way, I would answer: a long practice working with a buggy Windows software.