If you can't get them powder coated, I'd just go to the local auto parts store and get some black semi-gloss engine paint. It's probably $6 - $8 for a can. Take the parts off the bike, scuff the metal up as well as you can with some sand paper, find something to hang the parts (a metal coat hanger should work really well), then give them a nice light coat. Re-apply several layers, letting the paint dry between applications.
Although this method won't give you a finish that's as durable as a powder coat, you'll still have that can of paint ready for touch ups ;^)
Although this method won't give you a finish that's as durable as a powder coat, you'll still have that can of paint ready for touch ups ;^)