Wheres the best place to find one?

have you done Mjoll the Lioness's quest to find Grimsever or what ever her dear lost sword's name is? If not, the dwarven ruin (the name of it escapes me) has a lot of falmor wearing or at least having lootable helms.

They drop like crazy in any Dwemer ruin with Falmer in it. Mzinchaleft is were Grimsever is. There is also a room within that has a complete set of Falmer armor - the only full set in the game.