Disclaimer: I work for The OCR
If ivory is in such demand to the point that it has a large black market, why aren't there more attempts to domesticate and breed elephants for ivory? It seems like with selective breeding you could eventually breed small elements (that don't eat a lot and take up too much space) that have large tusks (and produce a lot of ivory).
They also don't require a lot of space just because they are physically large... They require a large amount of space because they are elephants, so making them physically smaller wouldn't be helpful in reducing their space requirements.
That's all with ignoring all the impossible logistics, massive capital investment, and animal welfare concerns.