Dwarven material oath ideas?

One of my players is a cleric who worships Tyr. By this point, he’s realized that he was more wanting a paladin than a cleric since he didn’t want to run full support. His argument was that he chose a war cleric, but that’s still mostly support. Either way, being the gracious dm I am, I’m letting him “forge” an oath with Tyr, similar to how dwarves in Norse mythology did (example, how Gleipnir, the chains that bound Fenrir, was made with the sound of a cats footsteps, the beard of a woman, the roots of a mountain, the sinews of a bear, the breath of a fish, and the spit of a bird). Any ideas on what impossible items I could have him fetch to forge his oath? It shouldn’t be impossible, nor extremely difficult, but a little challenging for a level 5 party.

I’m not sure what it is, but the name Hand of Justice came to my head. Maybe a literal hand of some kind, since tyr is missing one, or it’s a set of scales where each of the platforms is shaped like a hand. I’m also thinking something from a wolf, like the fangs of a dire wolf or a winter wolf, which at cr 3 a few of them will be easier to make a challenge at level 5, or just reskin a level appropriate challenge to be a wolf.

Whatever you go with, I would try and keep it (physically) adjacent to the main plot. You don’t want one character’s personal side quest to completely hijack the game. It’s ok to make it be an encounter or 3 to give them time to shine. But doing it for a long arc really puts everyone else in the back seat for a long time.

"The rigid steel of justice, forged with the flames of hatred in a forge found in the eternal sea". I would assume you could just make the most nonsensical names and put those together. I mixed ideas with some sort of noun, and then tossed it into the ocean. It should sound ridiculous without context.

To show their devotion to a one armed god, the sacrifice should be obvious. Lose part of their arm. For a time. A level at most. 

Have them run into a salesman, warforged, other devoted Tyr follower with two arms., etc. Have them tell, show, sell them a replacement arm. Possibly this replacement is prosthetic, mechanical or a gift of agreement of Tyr. The replacement might have a special property like, fire resistance on that arm or even the whole PC. Perhaps it can cast Augury X number of times per day for free. Maybe it can commune with Tyr once a month. 

Have it be something that is worth the leap of faith to be Tyr's follower and lose the arm. Use in game lore to have vague positive things come from the sacrifice, but don't tell the PC that they will definitely get their arm back. Make it a genuine leap of faith.

Recover a stolen Tablet of Fate.

Chains of Duty : forged from a promise never broken, the song of an owl, tusk of an elephant, and the skin of a shark.

Gloves of Justice: forged from the silk of a phase spider, the feathers of a harpy, the mercy of a quick death, and a fair judgement from a court of law.

Lock of Obligation : forged from the love of a son for his father, the beak of a bulette, glass formed by a lightning bolt, and the horn of a devil.