I sprinkle calcium on greens once a week, and TNT once a week. I also keep cuttlebones in all the enclosures which my tortoises (and turtles) love to munch on whenever they feel like it.
I only supplement the babies. I shake about a teaspoon of powder over their food in the bowl while I'm chopping it up. Then mix it all in. This big bowl of food is for about 10 little guys and the bowl lasts two days. The bigger tortoises have cuttlebone and they all live outside.
If I have only one baby to feed, I use just a pinch of the powder between my index finger and thumb over every feeding. But if they can taste it they won't eat it. So I mix it up real good.
You can also offer high-calcium foods to your egg-laying mama.