I have a customer with a Zinsco panel. I may need to add a 30A breaker for a dryer. I know Zinsco had (has) a reputation for breakers that DON'T TRIP! Also, the breakers in the panel are very small (even smaller than those GE peanut breakers). All the 'after market' Zinsco type breakers I have ever seen are quite large and quite expensive.
Suggestions or tips?

I bought a house last year w/a Zinsco panel in it & my home inspector said he wouldn't spend a night in the house because of it. So that was the first thing I had done to the place.

But that's expensive. One obvious idea is Ebay. I sold my old panel to, I think, Oregon Breakers in Portland: 503-736-0921. Another company here that sells hard-to-find circuit breakers is Dickenson Electric: 503-246-3550.

Best of luck
Jim

Zim, you hit the nail on the head. Zinsco is rather expensive to get breakers for. It is usually recommended to replace them. I have even seen cases where it is cheaper to install a readily available brand panel than to istall a couple of the obsolete style breakers. My advice would be to run away from an install that required working on a Zinsco panel.