Hello Marcus,
You don't give us much information. A picture of the tuba in question might help.
My first impression is that this is a used tuba of some kind. Small Couesnon tubas appear on Ebay regularly. Couesnon, at one time, was a very large company that made many types of brass instruments. It survives as a very small company in France known as P.G.M. Couesnon. They have this internet site:
http://www.pgm-couesnon.com/a_index.htm
There is not much content on the site, which can be read in both English and French. I don't think they make tubas at all today but I may be wrong. You may want to contact them and see if anyonw can help you.
Good luck.
Alex F.