How about this article (with cone equations)?:
http://www.nostalgiaair.org/Referenc...sh/Flash03.htm
My Atwater Kent Model 45 came with a Model E speaker, the cone of which was attacked by a squirrel! I was able to create a working (perhaps even good looking) cone using black artist's heavy rag paper stock from the local Michael's craft supply store. It isn't quite as cool as that impossibly thin plywood/veneer that they originally used--but it's neat, it works, and it bears up very well to casual scrutiny.
For a horrifying moment, I considered attempting to replicate the original cone's wood grain with "appropriately" patterned vinyl shelf paper....think 1970's station wagon**SHUDDER**.