It seems, I can check for the stock in warehouses from Lua, but I'd prefer to know the total of wares available or produced.
A callback that triggers each time a ware is produced would be one option. But having Player.get_wares would be useful, too.
P.S.: I'm considering evaluating my income tax idea in a scenario. So I need a somehwat working (doesn't have to be accurate) way to get player income.