Hi Andy,
I assume you mean the front suspension coil spring is broken?
As far as I am aware the front coil springs are not from any other car - they were made specifically for Bristol. Fortunately I have the spring specs, which Bristol kindly provided many years ago; this was for the 411, which has the same chassis as the 412.
This is the info you need to give to a spring maker:
306 lbs/inch +/- 15
spring wire diameter 0.625 inch
active coils 8.56
total coils 10.06
spring length should end up being 15 inches
If I were you I would get a pair of springs made and replace both of them.
Do you have the various parts that go above and below the springs? You can find pictures of the parts here
http://www.bristolcars.info/forums/8...on.html#post83
I bought these parts from Bristol Cars Services, but I don't know where you would get them from now.
Regards,
Kevin