Rob,
I've looked around from time to time, and have never found specifications for replacement circuit breakers.
I see specifications for continuous power draw in the Lionel service manual, but nothing that specifies the rating of the breakers.
For example, the section on 1033 transformers state:
"This transformer can supply approximately 60 watts continuously with continuous current load of 5 amps. "
But the tables in the Lionel 5F manual give the 1033 circuit breaker trip characteristics as 15 amps for 9 - 35 seconds.