In all probability, you will never know who made your lock. Even if you find out who made the lock the chances are very good that they have long been out of business.
As you probably have found, the Dixie Catalog doesn't show much in the way of sear springs.
Your Track of the Wolf catalog should be useful to you because all of the flintlocks they show are shown actual size.
Knowing that the pictures are actual size, you should be able to lay your spring on the picture to see if there is a spring that is very close.
Notice, I did not say "exactly like" your existing spring.
If you see a spring that is about the same, order a replacement spring. TOTW sells replacement parts for all of the locks they offer.
It may take a little grinding to make the new spring fit but with time you should be able to make it work.
Speaking of that, and the original post, you said you suspected that the existing spring is cracked at the U bend. If it is, and the crack doesn't go very deep, that is, it only looks like it penetrates in from the edge of the spring slightly you should consider removing it.
With careful filing, you can reduce the width of the spring just enough to remove the crack while leaving the majority of the springs width untouched.
Cracks in a leaf spring tend to propagate from the end or bottom of the crack and if this "end" is removed it will totally stop its growth.
If you do attempt to remove the crack, use some 600 grit wet/dry (black) sandpaper to remove all traces of the filing or grinding. The idea is to end up with a flawless surface without nicks or grooves.
Good luck.