This is my first post, so let me introduce myself. I don't want to get anyone's spidey senses tingling

I have been picking locks for just over a year and I am frequently on this forum for information. Usually I can find what i'm looking for with a search or 2 but I can't finding anything on what I am looking for now.
I have a number of old crappy lever locks that I have been picking lately with great success. I made a decent 2-in-1 pick with some copper and brass and it works great, I also use an overlifter that I made out of spring steel wire from a hobby shop.
2 of the crappy locks I have been picking do not have keys, one is an old 4 lever lock and one is a "Solid" 2 lever lock.
While learning and messing around with my 2 lever lock i noticed numbers on the levers when I opened it up. Is it possible for me to buy a key based on the numbers on the levers?
Any help will be appreciated, or if someone recalls a previous post on the topic a link would help.
Cheers
Dan