Willow structures are most common in the UK (fedges - fence/hedges), which is why most of what you'll find online is in the UK.
Most of what I've found is pictures:
http://creativewillow.com/
http://www.winterbournewillows.com/livingwillow.asp
http://www.englishbasketrywillows.com/index.htm - they're in NY and do workshops and sell kits
http://www.bluestem.ca/living-willow-structures.htm
Willow cuttings will take root if you plant them - so you just have to find a source for willow cuttings. We have a huge weeping willow in our front yard, so we'll probably take a bunch from that. I'm not sure what we'll do about the larger rods, we'll probably have to purchase them.