I would take a look at the artwork and decals that are available for the walls first. After you find your favorite muscle car, use that piece as a guide for your nursery theme.
Take your cues for color selection and decorative pieces from your framed print or wall decal.
You might make your own crib mobile using matchbox cars (if you can find some that represent your choice of cars. If not, cars in the right color might work), choose fabric to make a quilt in vintage car prints, decorate a plain lamp shade with cars or stenciled car graphics or get a car shaped area rug for in front of the baby's bed or your nursery rocking chair.
Due to limited or (downright nonexistent) selection of crib sets in your theme, you might have to shop for a solid color set but no worries since there are so many ways to jazz up the rest of the space in your theme.
When you're finished, why don't you send in pictures of your room to this website to help other parents that are having difficulty?
There is also a contest running on this sight under the "Free Stuff" tab where you can win $100 in wall decals and artwork that you might want to enter!
http://www.unique-baby-gear-ideas.com/babyboynursery.html