Thanks, Jamie and Ron, for your replies. It good to hear the voices of experience, particularly without the 'don't try this at home, kids' warnings.
How thick is the spring material? The spring from the backup camera seems to be 0.020". McMaster shows item 9036K217 - 1095 spring steel, 0.020" thick, 1" by 100' for $97.05. Does this sound like the right stuff? My Frankenspring, as I recall, was 0.010".
I guess I'll try pulling the spring out of the backup camera's case and anneal the end (both springs broke at the arbor). My real fear isn't getting hurt extracting it, but that it'll be difficult to get back in the case. It's always easier to make something into parts than make something out of parts.
If that works out, I'll see about replacing the Frankenspring.