Sambar stag is the densest, sturdiest, and widely viewed as the most beautiful stag for knife handles and other items. Due to rapidly dwindling numbers, its export from India (by far the largest supplier) is now verboten. Hence, most things with Sambar stag have leaped in price in the past 3-5 years.
I believe Sambar stag can still be hunted in New Zealand and Australia, and some of this material may be making its way into materials markets. But my understanding is that this stag is not on par with the quality that came out of India.
Several custom makers have stockpiled quite a supply. Most big manufacturers (like Boker, as indicated in the link above) have moved to using red deer stag, burnt bone made to appear like stag, and the like. For aesthetic purposes in "user knives," these alternatives are probably fine, if not quite as tough as Sambar. But for collectors, Sambar's value will only go higher and higher...
Glen