Garand Inho
Got a few possible options:
Rocho
Though not a mandalorian, he is a trandoshan. And while they do have different looks at honor there's still similarities, and Rocho respects mandalorians and their culture. Rocho often travels alone but I'd be up for doing some time working with a mandalorian using him. He is trained in the force, however this plays almost none into the way he act. Rocho believes in the Scorekeeper, and that success and risk are vital to impress. However he's not so convinced that failure is inherently abhorrent, if it was unavoidable.
He could also run into the Dar'Manda. He wouldn't care about that part, but it's plausible they could end up at odds or on the same type of mission.
Salis
she fits much more with your second character. She also likes killing and violence, and right now isn't in the best spot after loss of her husband. She's a much stronger and more dangerous force user than Rocho. And, because of her situation, is on a sort of "vacation" for now. It's entirely feasible she left Zweihander Union territory, put on a disguise, and decided to go kill something.
This character, Mariah:
Could fit with either really. Mariah is a tech expert but she's got a lot of experience in a wide range of things. She's been a smuggler, a cybernetics repairman, a droid repairman, an entertainer, all sorts of things. This is because she's 78, something that doesn't show due to a special artifact. Unlike the upper two, she isn't force sensitive. While she has had military training, she doesn't like fighting in person herself due to the dangers it causes, Instead she often tries other avenues OR uses a type of droid in her place (I submitted it today, hasn't yet been approved, just like her ship I made). Mariah could potentially meet with either one.
Garand: She couldn't tell him how to become a better mandalorian. But she might be able to help learn more skills, as well as aid him on hunts for a time. She has no issues working with other people personally, but she is very careful on who she trusts to go in her ship, or at least, where they are in that ship.
Hank: Probably a different scenario. She could maybe work with him for someone else, maybe trying to get some kind of cargo or something. Or they could be at odds. Harder to consider the scenarios here without having to do a lot of NPC's, something I'm not fond of.