An RTV somewhat soft silicon mold material would most likely to the trick, then use a relatively “rubbery” injection wax (not a hard, “crispy” wax) at least for the first tries at what wax to use (there are MANY, MANY formulations with all sorts of different properties).
When making the mold, a cut mold could be made (fastest cheapest and quickest) or make a 2 part mold via using a separation barrier between the 2 mold parts (or 3 parts if a 3rd section is needed to get easier wax removal). Then cast the wax(s) in what ever metal you choose. 3D printing might be an alternative but I do not have any idea of the cost. The mold as described above would be somewhere between $30-40 to $100, wax injections (once the wax type was decided upon) a couple of dollars each. Then the cost of investment and casting and of course the cost of the metal to be used in the casting(s). Without seeing the actual bone, I would imagine the bone structure is very thin in some areas and thee areas may need slight build up or thickening to ultimately get good waxes, some trial and error might be called for unless you can find someone with experience and knowledge in casting items with “large area” thin parameters, not a common situation in most jewelry. This is not an impossible job by any stroke, but it may need a bit of finessing to get good, usable and long-lived jewelry.
I doubt sand casting would work but then again I do not do small sand castings. Generally sand cast items are not real small, real thin or complex forms. Really fine detail/smooth surfaces common in jewelry are not usually or easily possible in sand casting just due to the processes and materials used in such work.
Hope this helps a bit.
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