The Pitt Rivers Museum has souvenir pens with a boat that floats up and down.
They also have toothbrushes with the same thing. The address is :
The Pitt Rivers Museum,
University of Oxford,
South Parks Road,
Oxford, OX1 3PP,
UK.

fax: 01865 270943

I hope this is useful!
Best wishes

Marina de Alarcon

Curatorial Assistant
Pitt Rivers Museum,
University of Oxford,
South Parks Road,
Oxford,
OX1 3PP.

telephone: 01865 270928
fax: 01865 270943