Needle in a haystack but, hey, you never know.

I think that Precision Manuals used to or may still sell them.

They used to sell a very thorough 747-400 manual designed for use with the PS1 747 simulator. Very top notch stuff.

Yes but they are out of them and have no plans to make anymore

Try getting your hands on one of the original PMDG 747 FSX/FS whatever copies.

The manuals are not quite the same but are very, very in depth and are good enough to use if you are trying to prepare yourself for the new 747.

Otherwise, if you have cash, splash on a copy of PSX which is the successor to the original 747 PS1 / PS1.3 simulator. If I remember correctly you get a set of manuals with the software. Those manuals are good enough to do anything.
I had a chance to fly a full motion 747-400 sim and was able to handle it easily including some wild failures thanks to all of the PS1.3 training and the documentation for it.

Hell of a lot of reading though. These days I sort of wonder if it's worth putting all the time into studying the 747-400 when the 747-8 and the 747 in general are being phased out in favor of twins like the 777 and 787. Don't think they'll be flying much longer unfortunately

Amazon has something: https://www.amazon.com/747-400-Pilot-Handbook-B-W/dp/0936283254

or if you have a couple reams of paper available

landrover.narod.ru/gershon/AIRPLANTANK/747-400_operations_manual.pdf