I have started to collect old padlocks and as many as is often the case, do not have keys. I thought I would try to make new keys for some of them or have keys made if the task is beyond my capabilities.

The problem that I am having and am trying to solve is that when I look up a padlock in an old catalogue they give a key number for a particular lock but that number is now outdated. So the question is how does one identify a new replacement key blank for that padlock from the old number?

As an example, I have an old YALE padlock #724 and in the catalogue #26 page 57 of the pdf it gives the #12 1/2 as the list number for that padlock.
So, my question is how can I find a new replacement key blank for this lock if one exists?
This is a general question and refers to other lock makers also.

Thanks for any insight into this pursuit.