Some people supplement with cat food which is usually about 35% protein to help with molt and stimulate egg production. Usually 14 to 16 hours of light is used to force them to lay through the winter, if your not getting 14 hours of light that is likely a problem.
Was last winter their first winter? If so, first year layers will often lay through winter, even without supplemental light. This is a first year only treat. Your birds may lay during following winters, but it will be much more sporadic, if at all. Rest assured, though. They will fire back up as soon as the days lengthen!
Oyster shells provide extra calcium for the laying girls, which is essential for healthy reproductive systems. Here’s the product I found works best, keep some in a separate bowl: https://www.amazon.com/gp/product/B00UIM7N0A/?tag=backy-20