For some ridiculous reason, my headlights (the plastic "covers") at the very front, are spider cracking, and they look terrible. i want to replace them, but i don't want to replace the entire headlamp assembly. is there some place where i can buy just the plastic pieces?

 

I don't think so, Look on E-Bay for headlights, New from Ford is around $125, E-bay used or maybe new or aftermarket around $50. You Have to remove front bumper cover to change out headlights, Go Figure,

 

Have you tried polishing the plastic lenses? Try some Meguiars Plastx or something similar. Try asking this question in the detailing section and I'm sure some one will be able to walk you through wet sanding and polishing the lenses so they look like new.