Hop plants are dependant on the amount of light they get during the growing season. As the days get longer, they use that time to grow roots and the bines. We just had the solstice, and they start flowering soon afterwards.
You won't find any place that sells seeds, because it's possible to get male plants that way and they are very undesirable. The female plants are the ones that put out the cones we use for brewing. Rhizomes are cuttings from the roots of the plant. If you planted rhizomes now, you may get a plant a few feet high, but that's about it. You wouldn't get any hops out of it at all this year.