Can I get a repair manual for a 1977 GE P7 double oven

You may be able to get a Manual from applianceblog.com, you will have to sign on create a username and password. But parts may be scarcely available for a unit that old. I share your angst as I had to give up an older unit a few years ago.

With it being as old as you are saying, about the only place you might have luck finding parts would be to check online at some used parts places. I tried checking Sears website but from what they were showing, you have not provided the full model number and I could not find out for sure if there were any manuals or if some of the parts were still available. Usually, after a unit has reached 25 to 30 years in age, if not sooner, parts are not readily available anymore. Sorry I could not help you better!