Making flat springs for obsolete actions is a service I offer. It helps if you have the parts of the broken spring, but it is not always necessary. Flat springs are made from a carbon steel that is shaped by hand to fit the action and then hardened followed by a temper.
Flat springs may be Flat like the one pictured above for an antique “Long Tom” made by Crescent Tool (yes the makers of the crescent wrench). These were designed to be sold out of hardware stores at inexpensive prices.
V-Springs are essentially flat springs that have been bent into a V-shape. These types of springs are very common in black powder locks and take more skill to produce.
To make and fit a simple flat spring typically takes 2 to 3 hours, and V Springs can take a few hours more due to more complex fitting and grinding.