Purchased one on-line this past March from Four Winds Growers in California, had it shipped to NY. Had a choice of a 1-year or a "2 to 3 year" tree. Went with the 2-3 year, it was sent bare root and it's happily flowering now. I also bought a 1 year Bearss Lime but wish I bought the older tree because it may be a strain on such a young plant to let the limes grow this year.
There are dozens of places to purchase a Meyer Lemon, I'm sure you'll hear from others!

Have you tried a lowes or a home depot? A couple of my friends farther south seem to find them there.

Fourwinds (online) is a good place. They're pretty pricy, though.

There are a couple of good sellers on ebay, but you'll pay about the same as you would from fourwinds. (if you want a bigger tree)