yes there is only ONE
try using this:
http://www.levineautoparts.com/upclear1uvre.html
it's moisture activated, so it'll take about 3 days (at 50% humidity) to cure out hard,..and probably 2 weeks before you can sand and polish it (yes, I said sand and polish rattlecan paint) it's fairly amazing stuff, not at ALL your typical spraycan clearcoat.
(there is also a true 2 component clear in a spray can from glasurit (scroll down on levine's page), but at $44 a can, I'd rather borrow/rent a compressor than pay that kinda price for 12oz of clearcoat)
I've experimented with the U-POL clear quite a bit (because I DID NOT believe a spraycan clear would be worth a crap) and it'll go over most any cured paint surface, any automotive type basecoat, acrylic lacquer, and polyurethane paints, and cures out suprisingly hard and durable, and like I said, after about 14 days, you can wetsand it with 1500/2000, and buff and polish it out.
the surface you spray this on MUST be FULLY cured out, or it'll bubble and peel, so if you want to top a rattlecan paint job with this, I would wait 30 days before topcoating with the U-POL, so thats the problem, by the time the rattlecan paint is cured out enough to clearcoat, if you rode it, it's now so chipped up you have to start over, and if you didn't ride, you just waited a month so.....
most "color shops" (autobody supply houses) can make spray cans with whatever you want in them, so here's what I would do if I wanted to paint my bike, and had no compressor: I'd get standard urethane basecoat put in the custom spray can (each can will cost you about $25), since the basecoat is NOT a catylized paint layer (there is no hardener) it'll spray just like fast drying rattlecan paint, and you can topcoat it with the U-POL clear after about an hour (at 70 degrees) so you get just about any color you can think of, and a hard durable clearcoat to protect it, and all for about $45 in paint (a can of base, and 2 cans of clear should cover a bicycle) and you wont have to wait a month.
you could also try one of the motorcycle paint suppliers online:
http://www.cyclecolor.com/ or
http://www.color-rite.com/
both places sell urethane basecoats in spray cans (not cheap tho) but avoid their clearcoats, both are utter garbage.
you'll also need primer (and get GOOD primer, do NOT put $25 a can paint over $2 a can primer, get the primer where you get the basecoat), sandpaper and whatnot so read post #15 on this thread for my painting a bicycle post (long):
http://www.bikeforums.net/showthread.php?t=382836
I admire those who try and paint on their own (it's how I learned) but there is a HYOOGE learning curve in painting, and a bunch of incorrect hype floating around so the two best tips I can give you are:
1) TEST PANEL: shoot it all on a piece of pipe first so any mistakes you make will be on the test panel, and hopefully NOT the bicycle
this is the best tip I can give you, and I hope you actually
DO it.
2) PREP: seriously, 80% of the paint job is the prep (read SANDING) so take your time and get the surface as defect free as you can BEFORE you shoot the basecoat and clear for best results.
sanding is a pain in the @$$, it's tedious, boring, messy and just no fun at all, painting, however is fun, fast, easy and neat! so the tendency is to hurry through the boring to get to the fun part and I'm sure you've all seen how that comes out.
the most fun of all is riding around on something you painted and getting compliments.
riding around having to explain why your bike looks like crap, even though you JUST painted it,............not so much.