As to how many lockshops have spare skeleton blanks and keys lying around, I do, though not nearly as manyas I pick u.
I got a few when I finished a locksmith correspondence course years ago, then bought a number of them and check out garage sales, a local flea shop once or twice a year and get a number of already cut keys from customers who need a piece of antique furniture unlocked but none of any number of other keys of the same type work that lock or any other lock, for that matter.
I ask the customer if those keys don't work any lock they have would they be willng to let me take them off their hands? I get a lot of "pre-cuts" that way.