Title says it all. I designed these cycling jerseys. They are very cool. The collar reads: "Peace, Love, Unity, Respect". £40 each, message me for details.
how close to that diameter does it have to be? if you're really adventurous, you could take two rims, heat up the joint, pull it apart, then reroll them to be semicircles of a much larger diameter.
Also, here is a size chart. Small, Medium, and Large are available.