I'm often asked where to get boning, hoop wire, and millinery wire for corsets, farthingales, and hats respectively. Here are a few links:
http://www.venacavadesign.co.uk/ http://www.farthingales.on.ca/ http://www.corsetmaking.com/ http://www.alteryears.com/ That last one is also a good source for SCA Period costuming patterns.
Plastic tubing from Home Depot also works for a lightweight alternative to hoop steel, and more closely approximates the look of the round reeds used in Spain. DO use heat to relax the coils before putting them in your hoopskirt. Lay the cut length out straight acrossed the floor and weigh it down with books, then hit it with a hairdryer. OR, let it warm in the sun by weighing it down in your driveway or near sunny sliding glass doors.