Thats right: Bone
With all the evidence against dairy, milk in-particular (lactose, caesin, inflammation, insulin stimulation etc.), and the rather simple conclusion that paleo man wasnt milking wild animals, where do you think a lot of their calcium came from.
Well here is a great way to get all that tasty bone into your day. Bone broths, slow cooking meat on bone and such are probably more 'normal' ways to to plate up your bones with greater calcium return due to using much larger amounts of bone (especialy for stock/broths) but here goes...
Once you have removed most of the flesh from the carcas, pul it apart into the biggest sections and lay it out flat on a cutting board. Use a meat tenderizer to smash the all the larger bones open, and at least crack the smaller ones, though they will just become soft and edible whole anyway. Place this in an oven proof dish lined with foil. Drizzle olive oil all over and a drizzle of water as well. I then sprinkle some chilli powder, paprika and cumin over the top.
Then place another sheet of foil over the top of the dish to seal it. Place in oven for around 50-60 min. From there take the top foil off, cover with cheese, then replace in oven with the grill on. Grill for 5 min or so untill cheese is melted. Perfect.
Add some avocado and sour cream and enjoy. Most of the bones should still have a bit of crunch, but easily chewed.
Now, quick calculation of say 150 grams of bone, with calcium making up 40% of bone, gives us 60gm of calcium + ~200gm from cheese = 260gm of calcium
True, most of this is from the cheese, so whats the point you say, well the bone calcium is highly absorbable in the form of calcium hydroxyapitate plus comes with other minerals such as phospherous, potasium and sodium.
Requirements for calcium levels have also been worked out on a grain rich diet, full of anti-nutrients such as gluten, fibre and phytates. Every test conducted to determine RDI's would have used a test population with exactly the same problems (anti-nutrient filled diet) and even encouraged to follow a "healthy whole grain diet" by the testers so as they could test mineral requirements when following a "balanced diet".
As these leach minerals from your GI tract, grains also cause gut inflammation and weaken cell bridges, causing 'leaky gut' and further adding to mal-absorption. Celiacs and those with auto-immune disease (and commonly irritable bowel symptoms) have a much higher incindence of osteoporosis, interesting! So, those on a grain free diet are going to need lower levels of most minerals. Besides calcium and magnesium content looks like it was over-estimated back in the day anyway. Check here and here. Just like cholesterol, calcium has quite a good self regulating system depending on dietary intake, and we all know what a crock the cholesterol theory turned out to be. Good amounts of protein are also improtant for calcium absorption, so dont listen to the old story that protein causes calcium difficiency. This has been proven plenty, but check here for an example.
So, enjoy your crunchy nachos, get plenty of dark green vegetables, some nuts, fish with bones, butter, cream, and...er...bones, for healthy bones