There are probably not commercial farms that sell cruelty-free eggs as described by you, but it's likely that there are many individuals who keep a few chickens as pets and do not kill them after their egg production slows.
For commercial farms, it's not commercially viable. Some back of the envelope math says farms would have to charge something like 4 times the price of normal eggs to raise hens and not slaughter older hens. If we simplify the problem by assuming egg production halts instead of slows, and older hens take the same amount of resources as younger hens to sustain, we get:
cost_of_cruelty_free_eggs = cost_of_eggs × ------------------------
≈ cost of eggs × -
≈ cost of eggs × 4.5
Since most people don't care that hens are slaughtered, they would opt for the cheaper eggs, and the very small population that would buy cruelty-free eggs (even many vegans would still be opposed to this) wouldn't be enough for such a farm to be viable.
My model for the cost of eggs is very primitive, but see this FAQ from an egg brand (in the US) that markets themselves as having humane practices and claims to love their hens. Specifically look at the question "What happens to the hens when they are too old to lay eggs?". They estimate that they would have to charge about 12.00 $ per carton of eggs, which is indeed about 4 times the current price of eggs in the US.
I've never heard of a cruelty free egg farm in the US, and I think this is the reason for it. Perhaps it's different in other countries, but I doubt it.
P.S. You may also be interested in the question titled "I’ve read bad things about male chicks. What happens at Nellie's?" in the FAQ. It discusses another animal cruelty caused by commercial egg production that you may not have considered.