You are correct, I did not understand the initial comment… I get it now.I think you might have misunderstood, or maybe I did. Buy one just like it, take the spring off the cheap one and put it on the Starrett one, then throw the remains of the cheap one away.
OR
Make your own replacement spring.
Keep the patina and use it for old tools
Go to antique stores, tools like that are very cheap as the market is flooded with them. Usually found in bins with many unrelated items.
Pierre