In season, you can order Hop rhizomes (root cuttings) from several places, online, and possibly locally. I got mine from Beer & Wine Hobby, located in Massachusetts, but they will ship them. I live in New England, so if that's Northeast enough, they grow fine here.
I ordered 4 (two each of two varieties), but only two sprouted (I think both Cascade). My fault, I suspect. These two are now more than enough for a good September/October harvest and brew session, and I usually have a gallon size freezer bag or two to share as well. The number you start with may help establish a usable vine sooner, but once one is fully grown, you'll have all the root cuttings you need to establish as big a hop garden as you need.
The proper time to plant is in the fall, about when a fully grown plant would be going dormant. They need to sit in the soil for the winter and will sprout in the spring.
The first few years there were only a few cones, but last year I harvested 3 pounds, enough for several brews. (And last year hops were at a premium due to a shortage and would sell wholesale for $26/lb!).
I have built an arbor, similar to those used to support grape vines, and train them up the trellis each spring. They grow up about 7 feet, then across the top another 5-6 feet. It's certainly not a typical way to grow hops, but it works well for me.
I had heard they could grow to 30 feet, so the first season I ran several lines of twine from the arbor to the peak of the roof, but it was completely unnecessary - a bit of pruning contains them well, and concentrates hop cones at a height I can reach to harvest.
I just moved, and have dug up several chunks of root and have transplanted them to a nice spot in the new yard near a shed. I'm hoping these sprout in the spring.
In my opinion, it's well worth growing your own.