Think they may be custom-built.
Searching for "kunstradfahren" and "kunstrad" may be more fruitful. This is a European sport. I've got my son doing a quick search on German websites.
My son's report below. I haven't tried to search through the links he lists.
"Hey here's some links to sites that sell those bikes you were talking about. Their sites are terrible and difficult to navigate though, especially if you don't know german or czech lol.
http://www.radsport-langenberg.de/
http://www.langenberg-fahrradmanufaktur.de/
http://www.langenberg-manufaktur.de/
http://www.fahrrad-walther.de/
http://www.otoupalik-bikes.cz/
http://www.starbicycle.com/
http://www.radball-mlady.de/
"I couldn't find any company in the US that makes them, mostly German. From reading around, it looks like a lot of people build their own. They are special bikes, here's a wiki site about em (in english, haha!)
http://en.wikipedia.org/wiki/Artistic_cycling
I hope that helps!"
I note that on the first site, if you click on the "Indoor" and then the "Kunstrad" link, it takes you to those bicycles.
Keep in mind, these sites are from web searches, and do not represent purchasing experiences or anything, so you're on your own there.