Well, there is that "sticky" article at the top of the Chicken Behaviors and Egglaying, but you've probably already read that as many times as I have.
When I have the problem you do, which I happen to have right now ... well a few more should be laying than are ... I pull out the big guns because desperate times call for desperate measures.
Here's what I'm thinking of doing:
I am going to supplement their feed (if I were buying feed, I'd probably switch feeds because sometimes the feed is old and then vitamins have gone bad). I will be giving them more animal protein to get them over the hump. You know, more canned fish, scraping from the scrambled egg pan in the morning, every last scrap of meat left on a plate, bones to pick, etc. In fact, I did this the other day and got more eggs the very next day. Hopefully once they all get to laying, I can cut back to normal because canned fish is a little bit pricey.
I was finally able to let them back out to free range now that they made their move to the winter coop. So more green grass to eat and wider variety of vitamins, minerals, etc., from live feed.
I also expect that they have calmed down a bit and have settled into their new home after being there for two weeks. Non-stressed chickens lay more eggs. I will be evaluating to make sure they aren't stressed. You know ... enough nests, not too many roosters, no overcrowding, no huge drafts. A family of coons moved in about 3/4 of a mile away, but I doubt the coons are spooking them because I don't think the coons come around here at night. The coop is coon-proof (I think. I hope those aren't my "famous last words.")
I have never given the layers supplemental light over winter, but I am tempted at this point since I am not sure what the deal is.
I would consider the breeds, but over the years I have purposely bred together roosters and hens that have done very well for a number of winters here to make a hardy group of chickens. I am sure I've got a winter-hardy group of hens ... at least the ones I hatched. I guess that I have about 7 hens that are unproven, with the Russian Orloff and Faverolles being known for not always laying a lot of eggs and sometimes also for being slower to mature.
I have also looked them over for mites, but they seem free of them.
A few of mine weren't hatched until the beginning of June, so that is part of my problem, but most were all hatched in April and early May.
Years ago I got a bad batch from the hatchery. They never laid well. They were held up in the mail somewhere. They arrived listless, but I got them to perk up. Then they got pasty bottoms. They had a really bad start and never did lay well no matter how much I tried to help them.
Oh, and I will up their cayenne intake. Their feed already includes it, but in the past a little more has sometimes given them a little boost to get them laying--about a tablespoon a day for 10 hens or something like that is what I sprinkle on top of their feed for the day. It sort of works as a tonic.
Are your hens' combs and wattles all bright red?