This project is one of the many that I have put off for YEARS, which is unfortunate not only because I'm an expert procrastinator but also for the fact they came out great.
First of all, you need some tin reflectors off of the eBays. They look like this...
They come in all sorts of different sizes and types and it doesn't matter if they are rusty or not, you're going to be painting them. The good thing is that they were not that expensive when I got mine.
Next, you need a base coat of spray paint, to match whatever color glitter you want. If you want black glitter, you need gloss black paint (although, you do realize that black doesn't reflect light). I used orange but I tried silver too (didn't work too well).
Paint the reflectors with the gloss spray paint, both sides. I paint the backs, let them dry and then paint the "good side".
Be patient and let the paint cure for however long it takes (usually 24-48 hours).
Next comes the fun part...spray them with glitter!!! I have tried the Krylon and the Rust-Oleum brands and I have to say that I like the Rust-Oleum better personally. However, I have had some trouble with spraying the product out; the can has a tendency to clog. I have had luck with short bursts of spraying instead of one long spray and immediately turning the can upside down and spraying a bit to clear the nozzle. The glitter is orange, the carrier spray is clear so that is why we painted the reflectors orange. You may have trouble finding this color, I did and had to order it on the ebays or Amazon, I forget which (note-I have noticed that a LOT of my eBay purchases are being shipped via Amazon so check the price before you order something, just a heads up).
Next, spray a coat of clear sealant on the reflectors. Not only will this protect them from flaking and dulling, they will look all the more shiny and shiny is a good thing!
This is what I used, available from your local (hopefully family-owned) hardware store, worked wonderfully.
Now, once they are all dried and pretty, you can put them on your C9 light strand! If you can use LED, more power (or less in this case) to you, I couldn't find any orange LED C9 light strands so I bought some orange C9 bulbs online and used them. I would much prefer LED not only for the energy savings sake but also for the heat, standard bulbs put off a lot of heat and can melt cords and other stuff if they are touching them. Most C9 cords have 25 bulbs to them BTW. So there you have it, don't put off this project like I did for 4 years (yes, it was 4 years), go ahead and make something pretty!