What you want, I think, is for people to see what you have. Then they will contact you with what sizes they want, when they want them. As long as you always have a mix of size around, no problem.
Years ago I worked in a pet shop. I raised mice; people came in for baby mice of assorted sizes - some wanted pinkies (newborn), some wanted them just furred out, and so on. They would call or come in with a request; I would bring in the right number & size the next day and they would come pick them up. It must have been excellent for the snake owners, and it worked well for me too.