So I've got Ancient: Manticore, Valla's, Natalya's, Danetta's, Greenstone's, Karlei's - basically everything except Yang's. I've been re-rolling an extra I have using the bounty mats recipe in the cube.
I've also done blood shards because I didn't feel like thinking.
A friend told me I should be upgrading rares for it, and I've done some of that but no dice. I wanted to see how other folks are getting theirs.
I tried the yellow to legendary reroll and got a few regular Yang's which I then used one of to try and reroll into an Ancient. I ran out of mats somewhere in the 20s of the reroll, went farming and found my ancient. So as stated, RNG is RNG but the legendary reroll will be your best option.
You need on average 10688 bloodshards for one Yang's Recurve; that's roughly 107k bloodshards for an ancient one.
You need on average 181 Death's Breath for one Yang's Recurve; that's roughly 2000 (and 4k of each other mat) for an ancient one.
You can run bounties and re-roll one; for 10 re-rolls you'll need 5 entire bonus bounty runs on T10 plus 500 Forgotten Souls.
I'd estimate about 1.5 to 2 hours for the bounty runs, and 2 to 3 hours of T10 rifts for the materials (and way more hours to get the bloodshards).
So TL;DR: Bounties > upgrading rares > gambling.
However, I personally can't stand bounties, so my rule of thumb is the following:
If the item is around 200 DB upgrade cost, I'll upgrade rares (2000 DB to get an ancient aren't that much if you're using a Sage's Set on wizard to farm T10)
If the item is an armor item and relatively common (like set items) I'll also gamble for them - it will give me an additional chance plus the rares that I can later upgrade, so I don't need to craft them
I only run bounties for very rare items that can't be efficiently upgraded/gambled but are very important, such as Wand of Woh.
I've been superlucky this season (or unlucky..). I've died about 6 times with my UE DH in hardcore this season but I've always been able to get an ancient yangs pretty fast after. 4 of the times it's been through upgrading rares. The other 2 by rerolling a non-ancient. I never spend blood shards on weapons because I dont feel like the price is justified. I rather try rolling ancient armors for the blood shards instead.
Upgrade rares. Once you get a non-ancient one then reforge it if you have the souls. If not keep farming dbs and upgrading rares.
Gamble for a few 2 handed weps just to tell the loot system that's what you need, but don't expect to get one from Kadala.
No ancient after 30 reroll correspond to 4% chance of that to happen. Bad luck but not unreasonable unfortunately. Keep going. I prefer upgrading rare to legendaries, yang is not that rare, and you'll get other bows as well.