When Can You Buy Weapons in Assassin's Creed II?

From the very start—as soon as you reach the first Blacksmith (▲ icon) in Florence during Sequence 1.

Weapon Categories Available

• Swords / Heavy Weapons / Daggers / Maces / War Hammers – melee.
• Hidden Blade upgrades – story-gated (second blade at Sequence 4).
• Ranged: Throwing knives (buy pouches), Pistol (unlocked Sequence 6), Poison Blade (Sequence 8).
• Armor: Leather → Metal → Missaglias → Altaïr's (collect all 6 Assassin Seals).

Progression

Better gear unlocks as you renovate Monteriggioni shops and advance the story. Money becomes trivial once the villa treasury is maxed (~Sequence 6).