Aha, well, you're an old hand at this so you won't have any trouble! Here's one source of replacement cones. I have no connection with them, just found them by a search. They have a $10 minimum so you could get a few more things besides. If you look around you might find some other source that you like.
http://www.electronix.com/catalog/de.../cPath/362_369
Here's a tutorial on how to accomplish part of a repair. Some of this doesn't apply to a vintage speaker.
http://www.decware.com/newsite/refoam.htm
If the cone is mostly there and just needs to be repaired, that can be done with white glue and pieces of coffee filter paper. I like to use fabric glue, available at fabric or crafts stores. It is similar to "Elmer's" but stronger and remains somewhat flexible. Some of this mixed with a little water makes a good reinforcing paint for old cones that are crumbling.
If you have to replace the whole cone, cut the old one off around the voice coil leaving about 1" of the old cone all around. Shim the voice coil as in the tutorial paying attention that the spider remains flat and then cut and fit the new cone to overlap what's left of the old and glue into place. Next day glue the surround to the speaker frame without pulling it or twisting it and let dry fully before removing the shims. During the whole procedure care has to be taken so that no stress is put on the cone to bend it to one side or the other, so that when the shims come out the voice coil drags. The voice coil needs to be free to move in and out without rubbing.