From Valve Developer Community
This unfinished weapon was scrapped before Half-Life 2 was finally released. Left-over Half-Life 2 source code shows that there were to be two ammo types for this weapon: a rock and a beer bottle. The source code shows that there was originally to be a view model for each throwing item. At least three models are missing for this weapon.
It is also in the source code commented that the ammo-handling code was 'a bit bogus', and needed a real solution if the brickbats were going to live to be released in Half-Life 2. The code was obviously not improved enough to make it.