you know fcp.co, with its loooong list of free plug-ins?
the 'effects' section lists some 'film looks':
or, you spend a day (or two ) at
and create your own 'looks' .........
I'd have to start by echoing what Tom said - the color tools in FCPX are well capable of creating a "flim look" and fixing color issues - which is all you've said is required.
I'd start with effects like "Dry Heat" and combine it with other effects and coloring.
3rd party tools are only going to give you similar presets that won't work in all cases, and you'll have to do the same thing. That is, you still need to figure out how to color properly whether you get 3rd party tools or not.
Having said that, I use Magic Bullet Mojo, because it ultimately combines many useful "Dry Heat"/filmy type effects into one and is sensitive to, and has several special parameters, for getting skin tones right.