Stupid question:
It is it not just a normal spring bar of the required width? (Some times they are shoulderless bars)
All older clasps I have use a standard spring bar.
If you pop put a picture of both the clasp and the bracelet end where the bar is missing, we might be able to give better advice.
Edit
I thought I would double check by taking a generic bracelet I have to hand apart
It’s a normal spring bar
I am presuming the Breitling would be the same