Paint Supply
http://www.autobodysupply.net/
They carry RM Diamont, which is a premium paint that can be matched to your car.
But warning, paint can carry UPS Hazmat charges of like $20 in addition to shipping. Watch out for that.
I find it easiest to run across the street to my local automotive paint supply store and get a bit mixed up. It's "more expensive" than online prices, but I pay no shipping or hazmat charges, and I have it right then.
You might look around, we have paint shops all over the place here. I do order my supplies online though. 
