6 levels? A human barbarian can get Diehard at level 1, and others can at level 3. If you have other feats you feel are more valuable, then you'll just have to wait. Unless you're playing mythic, anyway. Or maybe there's some magic item that duplicates Diehard or ferocity.
Should probably be under Advice not Rules, but eh.
Half-Orcs can get Endurance for free by trading out Intimidating. But perhaps better, depending on what exactly you want, is the feat Ferocious Resolve. It grants the Ferocity monster trait, which is Diehard by another name. It requires being an Orc or half breed as well.
Past that, I've had DMs allow feats that build off magic items. For example, a Scarlet and Green Cabochon ioun stone grants Endurance. Your DM may allow the same - to let you simply take Diehard if you have that stone. Drawback is if you ever don't have it, you lose both feats since you'll be missing a prereq.
You overvalue Die Hard. Raging Vitality and Toughness don't require you to be Staggered to take advantage of them.
Also, from my experience, Die Hard might as well be called Please Kill Me. One of my fellow players in Wrath of the Righteous invested in Die Hard. Every single time he's used it, it resulted in him dying. Every single time the GM admitted that if he'd been knocked unconscious, the enemy would have gone after someone else.
You are basically trading your safety net for the hope of getting an extra attack or two in, and it's usually a bad trade.
Talisman of the Orc Mother's Fury is a neck slot item granting ferocity or enhancing ferocity or die hard.
Hobgoblin Battle Standard, though too expensive..
Never Stop Shooting trait, kindasorta
Flagelant cleric 2, by Kobold press
Bedlam seeker barbarian, an urban steampunk barb from Pure Steam (3pp product)
Shogun samurai 4, by Rite Publishing
Of course you could use Diehard and don't continue the fight. Act as if disabled/dying, crawl away, quaff a potion.
Ring of Ferocious Action helps with the staggered condition btw.
The Heart of the Wilderness human alternate racial trait should be mentioned too.
Thanael makes a great point, and basically what I'd consider the best use of Diehard - ask your GM how hard it is to pretend to be knocked out (they'll probably say it'll be a Bluff check, so if you haven't invested in that skill this might not work).
Using Diehard to get yourself an extra action to heal yourself so the healer doesn't have to is a great use of it. But using it to stay in the fight on your last legs is really dangerous.
Yeah, raging vitality and toughness will both keep you in the fight longer without the risk of killing you.
Oh, that said, as a barbarian there is another reason to take Diehard. When you fall unconscious, your rage ends. At higher levels, this will cause you to lose enough hit points that you probably die anyway. So at that point, taking Diehard to keep yourself conscious will save your life.
Except Raging Vitality lets you Rage while Unconscious anyway. =)
Thanael makes a great point, and basically what I'd consider the best use of Diehard - ask your GM how hard it is to pretend to be knocked out (they'll probably say it'll be a Bluff check, so if you haven't invested in that skill this might not work).
Using Diehard to get yourself an extra action to heal yourself so the healer doesn't have to is a great use of it. But using it to stay in the fight on your last legs is really dangerous.
Yeah, raging vitality and toughness will both keep you in the fight longer without the risk of killing you.
Oh, that said, as a barbarian there is another reason to take Diehard. When you fall unconscious, your rage ends. At higher levels, this will cause you to lose enough hit points that you probably die anyway. So at that point, taking Diehard to keep yourself conscious will save your life.
Unless you take the Guarded Life rage power. And half-orcs can fight with Diehard until they die no problem. Just Take Tenacious Survivor. The healer doesn't even need deathwatch, he will automatically know if you go down you are dead and he only has a few rounds to heal you so you can come back.