Any body shop store will have paint and they can mix it any color you want.Just look in the yellow pages under auto body supplies. The easiest (and cheapest) to use IMO is an enamel single stage (meaning just color coats no clear and it's ready to go).Laquer is easy to use too but might react with the paint underneath and it's getting real tough to find. A basecoat/clearcoat will give a good finish also that will hold up well. It's all in how much money you want to spend.Mix according to instructions or ask the person there. They will know. If you are going to go with enamel pick up the reducer that matches the temperature range in your area on the day you are going to paint.It's not as hard as it seems just some reducer evaporates faster than others according to temperature and you don't want a fast evaporating reducer on a real hot day ot the paint will look dry when finished,nor do you want a slow evaporating reducer on a cooler day or the paint will run easier.You can get hardener to make the paint harder for a tougher finish and more shine, flex additive for urethane parts, and flattening agents to make the paint look as flat as you want.
I prefer DuPont or PPG paints myself though I have painted cars using Western enamel paint I picked up at a surplus place and had good resaults with it. I have a local place that sells DuPont paints also so if I need a color mixed I would just go there because it's local.If you go with an off the shelf color (most the time they have black in pints,quarts,and gallons off the shelf) pick a body supply place that's fairly busy so you don't get a can that's been on the shelf forever. Always always,I can't stress this enough, filter the paint through the paint filters they have there before you put it into your gun.They look like paper funnels with super fine screen in them.Trust me on this one.
I'm a cheap ******* so I usually go with the cheapest route. Most small parts you can rattle can with good spray enamel paint and they will look good.Most the small parts on bikes stock are a semi-gloss black to begin with.What i found to work real well when I was painting my small stuff is to make yourself up some wire coat hanger hooks bent at 90 degrees or a little more to hang the stuff from the ceiling or use fishing line.I do wipe the parts off with something that will remove all traces of oil and fingerprints. Either a surface prep chemical or enamel reducer or laquer thinner on non-primered parts.
Do yourself another favor when you are at the body shop supply store pick up some disposable screw on air line filters and put it on the inlet on your gun. They are lifesavers in places where you get water in your compressor and don't want it coming through the airline and into the paint where it will make fish-eyes or bubbles.They are usually plastic and sphere shaped about 2" in diameter with male threads on one end and female on the other that mtch the fittings on your gun (I think it's 3/8 NPT fittings on air lines).
I have a Sharpe Cobalt HVLP gun I use for fine finishes like car bodies and I'll probably use it to paint my tank and I have a small touch up gun for the small stuff that works well for that but to be honest I used rattle can black for a good bit of my small stuff and even the frame on my CB.If you take your time and use decent paint (not the $2 a can **** that disappears when it contacts gasoline) and aren't worried about 100 point concourse restoration it will come out nice.You would be surprised at how far spray paint has come.The next one I do I'll use the spray gun just to see if there is much a difference.
These are just my opinions on paint.