Find a local junk yard and they should have a bunch real cheap. I went with a picture of one to show them what I was looking for and they showed me a pile of them and said pick what I want, $30 a pair.
Just pay attention because some of the covers have the same style oil cap as the GN's and others have the TTA style, I accidently picked up a wrong one once without realizing.
HTH,
Steve