Heathkit manuals are like Gottlieb manuals. They are still protected by copyright and the current owner of the Heathkit copyrights actively enforces those rights.
Here is the official Heathkit manuals website where you can buy the manual:
is there something particular you need to know from the manual? the manual itself is just the build instructions. the user instructions are on a sheet pasted to the inside lid. my 5320 has both and i could look something up for you though i don't have time to do a full scan anytime soon.