Try polishing them. Clean them, sand and then use a bench buffer and compound.
I start with a 3-M metal finishing pad to smooth the surface then work down to 400 grit paper. Then it's the buffer and compound until the aluminum starts to shine. Keep working and you'll end up with parts that closely resemble chrome at far less cost than having them plated.
Due to EPA regulations you might have trouble finding a chrome plating shop. Most of them have gone out of business and those that are still around have gone away from the old 'triple plating' (copper, nickle, chrome) that they used to do. What's out there today is a single layer chrome job that doesn't look or last like the real stuff used to.
Aluminum castings can be polished very nicely with a little work.
Tom
