Funny you asked. I'm a plumerias junkie.
I have over 30 plumerias some are named cultivar that are rooted or from cutting and few from seedling.
I've been collecting over 2 years. Let me tell you they can be very addictive and expensive hobby.
I buy mines from Plumeria Society of America. They are the real deal.
You can buy from others but you have to be careful cus sometime you will get the wrong flower and over price.
If you just want a plant then you can buy from anywhere. I know Lowes and Home Depot sell them.
believe it or not.. theres over 100's of varieties plumeria aka Frangipani
Very easy to take care but do better in zone 9 .. like CA , TX and FL
but you still have to keep them from freezing temperature.
I keep all my in black containers some are dig into the ground and during dormancy season(winter time) I bring it into my garage.
It can be a pain in the butt, especially when you have so many to dig up.
but its worth it when you seen these beautiful flowers bloom.
you can read and learn more about plumeria here
http://www.theplumeriasociety.org/