http://www.alohatropicals.com/Plumeria.html
http://www.exoticplumeria.com/
http://floridacolors.com/
http://www.kimisplumeria.com/
http://www.mauiplumeriagardens.com/index.php?cPath=1
There are also some reliable sellers on Ebay. I'm sure there are many others but these are the ones that I'm familiar with.
Hawaiisandy
scubadiveandfish
emersonsambassador

You will have to winter your plumerias over indoors in your zone. One factor that determines when it will bloom is where the cutting was taken from on the original plant but someone with more experience will be able to let you know what else contributes to when it will bloom. I've had some cuttings bloom the first year and others take a couple years. You might want to spend a little more and buy a cutting that is already rooted. Sometimes cuttings can be a bit tricky to root.
Karyn

Karyn- that was, as Gill would say, "spot on." Great advice!! Bill

I have also had very good luck on Ebay. I shop with these sellers. I live in southwest michigan and I have rooted (on heat mats) In my basement some beautiful plants (also have my first inflo). Check out peoples feedback and really read some of them. Most of them will fix anything that goes wrong. My packaging from these people was awsome!
evelyn2079,hawaiitropicals75,subadiveandfish,hawaiisandy,& plumeria-addict.
Hope this helps you.
Valerie

I enjoyed the business of: http://www.mauiplumeriagardens.com/index.php?cPath=1

They packaged my three cuttings in a professional way. They also gave me a three tip "mystery" cutting for free! How sweet is that?

I requested that they ship the cuttings on a Monday and they followed through with this. They also emailed me to let me know what was going on with the shipment.

I would second (or third!) the Maui Plumeria Gardens site...I've ordered from them at least three times, and they almost always give me a mystery cutting along with what I order, and this time I got a 3 tipped rooted cutting instead of the 2 tipped rooted cutting that I paid for! Guess that says volumes about my customer loyalty and about their customer service! :)

Aloha,
Mark