Achmed/Achmed's Axe and Arrow. He's a weapons dealer who can teleport his shop to any of a number of places on the continent. He curates the best stuff, though he's a bit pricey, and has capitalized on the adventurer market. He's about the only source who can also afford to buy/trade magic items.
Ali Al'Ras'Gul... ( "A little rascal"? lol) His colorful tent is almost always set up in the marketplace of any city the party is in - even if they just left him behind in the last one, lol. He's the quintessential stereotype of a sleazy fast-talking used-camel salesman, and dresses in color combinations that make the eyes bleed and boggle the mind. Visually, he's sort of based on the prison warden from the first Brendan Fraser
The Mummy movie.
He sells anything listed in the PHB, as well as other common items that an an adventurer might want. He always seems to have what the party needs, or what they will need but don't know it yet. He also seems to be able to get the party... other things. (If the party could just see their way to doing him a small favor, of course...) He just happens to have whatever common magic items that the party might want, and ether can get or knows where to find the more uncommon ones. He always seems to know things he shouldn't, but always doles out information in cryptic ways, and usually trades in favors rather than cash.
The back room of his tent seems to be much larger than it should be, and it is. It's actually a nexus of doorways to other places, including the City of Doors. Ali himself is also more than he seems (and sometimes less). But nobody seems to know quite who or what that actually is. He's well known amongst the more powerful beings for being an instigator, a dabbler, a meddler, and an incorrigible agent of chaos. He's always scheming, plotting and playing an angle, and even beings such as the Lady of Pain are often left wondering just what he's up to...