Slitherine

I am a bit surprised to see that the skirmishers can throw javelins all the game long. Does it means that they can resupply from an invisible bagage unit (visible in some scenarios) ?

Is it the same in the tabletop game ?

The TT game dose not bother keeping track of ammunition supplies for javelins or bows. So yes you can chuck away to your hearts content.
Not sure its anything to worry about where the ammo comes from, I would assume the resupply corps would be in such small units as to not be worth representing in the game

I think in general only a small fraction of each unit would throw their javelins in any given turn so as to conserve ammunition. Also, I think the game is more designed to give 'feel' than it is to be a strict simulation (a wise choice in my view), so what is say ten turns of javelin chucking on the hex grid may not in fact represent ten volleys of javelins in real life anyway, rather the cumulative effect would be similar. So in effect it's fine as it is.