A collection of tandem unicycle riders found on the internet.
Corbin has built a tandem unicycle and ridden it together with Scott. Here is a nice instruction on how he built it.
There must be a tandem unicycle somewhere in Hannover which is ridden from time to time:
Klaus rode the tandem unicycle together with Nelson during the EJC 2011
Some other tried it as well:
There is a rock band called “Tandem Unicycle”