I've set up a new party, with one character armed with a bow, one with a crossbow, two with melee weapons, and I'm hunting thieves in the streets of Schleswig. However, when I find them, "Ranged Attack" is grayed out for both characters.

I experimented with equipping characters with javelins, though, and found they could do ranged attacks fine. What am I missing?

Ammo?
Arrows for bows, quarrels for crossbows, and balls for guns.

Ammunition, by chance? Bows, crossbows, and handguns need something to fire.

Bows - Arrows
Arbalests, Crossbows - Quarrels
Handguns - Balls

Edit - Well, there's two responses for the price of one!

I thought that might be the case, but I didn't see anywhere to buy it. Where should I look?

Many thanks to all of you!

(Sidenote to new players: the inventories of merchants are generally much larger than the single screen you see at first -- click on the bottom edge of the scroll, or press the down arrow key with the fourth item selected, to see more of the inventory.)