Hi, James, welcome to the message board. If you search the forum for "Eureka", you will find lots of information about these clocks. However, finding a balance spring will be more difficult. What is wrong with yours? Post a few pictures of your clock so we can see what you are up against.
The balance spring has been remade from what looks like piece of perhaps an alarm clock or large pocket watch spring?
This has subsequently had another piece soldered on to it. It is successful in that the clock runs; albeit erratically and way too fast.
The outside diameter is much larger than an original spring and looks all wrong.
I would really like to get a replacement spring made, but realize that this may be problem.
I have the specifications of the original springs, but matching the modulus of an original to get the 2 2/3 oscillations may require a lot of luck.