There are about a dozen separate missions available in the FS2 GOTY mission pack (modern MediaVPs use this mod by default), and about thirty in FSPort (or was it in Silent Threat: Reborn mod? Can't remember). They should be accessible from the Tech Room when you launch their respective mods.
As for other mods, I don't think there are ones created with single missions in mind available on Knossos. But I'm pretty sure Blue Planet had a bunch, some of them were remixes of the campaign missions and others were a sort of separate scenarios, for the funsies.
You might also want to take a look at Just Another Day: Extreme Arcade, it ought to have some of the feeling you're going for.
Although I recall that none of these are the massive battles you mentioned. Well, there's one in BP.