Thank you
Ridgerunner, very thoughtful and thorough as always. I would only consider the first three options on your list anyway. I would not get chickens of any age from local flocks, auctions, swaps, friends, farms, breeders etc. I just don't trust their biosecurity measures (if any... lots don't have any).
I was considering hatchery chicks from a feed store vs. mail ordered, only to avoid the inevitable casualties of shipping and any additional exposure while going through USPS. I'll have to weigh that against exposure at the feed store itself. The one factor that makes me lean towards feed store is that the one local store I use, does not have chicks in open bins or cages out among the gawking and swooning customers, the way
TSC and some other feed stores do. Way back since before avian flu, they've had a policy that chicks stay behind the scenes, and when you walk up to the counter and ask for what you want, an employee goes back there and assembles your box of chicks, then brings it out to the counter. Which makes me feel a lot better. Random customers with their dirty boots and hands don't go anywhere near the chicks.
The best route is hatching eggs, of course, but they are very hard to find where I live. I either have to drive for hours, or mail order and deal with low hatch rates, higher cost, and a higher percentage of unwanted males. I've done that for breeds I really want, but in this case I just want some regular layers.