They are pretty small and almost all of the old models have them.
Used as a normal missile weapon, perhaps a regular bow would be a better match - less powerful than a normal crossbow and faster to shoot.
If you want something that can be used by more different soldiers, you would have to make it some kind of optional item you could acquire for them along the way... Not sure if there's anything that works there - are potions of the "explosive cocktail" type still a thing? (I know the potion table was revised in a supplement and in the 2nd edition). The molotov cocktail may seem a strange representation, but it's one of the few missile attacks that can be added on, and I could envision it as representing the soldier emptying a magazine into all targets within a certain area once per game. The medium range fits nicely there. Getting a bunch of these potions wouldn't be too difficult if you start with the brew potion spell and buy a few of them between games (they used to be fairly cheap at least, don't have the new rules at hand yet - assuming you are talking about the new edition that is).