I’m not that familiar with Bone Marrow; however, I’ve seen a lot of info on Bone Broth on youtube. I found a vid about making your own Bone Marrow. Don’t know if it’s what you’re looking to do but might lead you in the right direction. I suggest that you go to youtube & do a search for “how to make bone marrow” Then you can choose the vids that seem to fit your ultimate goal. You might also want to check out the Bone Broth vids too. For me, the Bone Broth looks easier to eat than the Bone Marrow & the Broth is supposed to be close to the Marrow health wise. I do know that the marrow is inside the bone. The carcass from cooking a whole chicken has marrow in it & the Beef Shank you mentioned will have marrow in it. You just need to learn the best way to extract that marrow for your particular use. My local grocery store sells Soup Bones & I’m assuming that they still have the Marrow inside them. Talk to one of the butchers in the meat market of your favorite grocery store or talk with a local butcher at their shop. Either of those should be able to give you some info on how best to find your Marrow.
Not seeing your initial post, this is the best that I have to offer!!!