You could try Aragonite calcium from chewy - there's not much difference between the "fine" and the "coarse" but I've used the fine in their wet mash that I serve every morning. But also consider that this could point to other problems, like absorption issues where other foods are blocking the...
I've tried that one - back when Manna Pro was giving out coupon books every year - my girls didn't care for it, as almost everything was too big & hard! I'm liking Flock Party Garden Grains at the moment, with added Black Oil Sunflower Seed.