Animals will use Calcium and seek it out when they need it. Most layer feeds have Calcium in them. Even if they don't look like their using it they might dip in once every few weeks. Keep it available.
Any bowl will do, just build a wooden frame (the same height as the bowl and heavy) around it so they can't knock it over. Easy, cheap, effective. or you could take that one step further and just build them a flat bottomed box.
I add grit to the food, mine are too young for calcium yet but I'll add it in the baby feeder when time comes. This way they can get it when they want it and it won't spill. You can get the baby feeders really cheap like 2.00 for bottom piece 2
00 for top piece. Comes in handy for stuff like that. Hope this helps.