Hi. One of my pullets (9 mos) has been having soft shell egg issues. She is fed layer feed (organic from a local mill), crushed oyster shell, grit, kitchen scraps, yogurt, BOSS and ACV (in water). After a trip to the vet, it was suggested that this hen may have a vitamin D3 deficiency. I've been searching for the best supplement. What do you recommend and where do you get it? Thanks.