A boxed set of flying monkeys?
I have to admit that I'm not familiar with the others, and not at all versed in the further works of OZ
There is a war game that has a flying monkey horde, so that would be the logical chose I suppose, but there are quit a few other armies and critters in the OZ verse, including: the evil gnome king's army, the forces of china town and other townships, Ginger's army of female liberation (they were armed with knitting needles but you could fanfic it up a little and give them rifles or medieval weapons), OZ's army of officers, and those are just the ones I can put names to there are just tons of armies and potential armies in the books.
One could easily do a mass combat game in the OZ verse with the only problem (which may not be a problem if you play your cards right) being that OZ is a soft fantasy setting where people can't die regardless of what happens to them (in other words it would be the perfect setting for a mass combat game for kids vs. parents game night). OZ wouldn't be my first chose for set idea (You all heard what those where
) but it is a setting I would consider doing if I had a malleable rule set and investment money.