I don't speak German so can't search for one there. Help!
Frindon5 After a quick search I found two websites that offer used wheelchairs and mobility scooters:
http://www.rollstuhllift-discount.de/
http://www.hilfsmittelboerse.de/
Although the sites are in German, I am sure that if you email them, somebody will be able to answer you in English.
Also, here are some words that might be helpful if you want to search on your own:
Rollstuhl/Rollst眉hle - wheelchair/wheelchairs
Elektroscooter - mobility scooter
gebraucht - used/second hand
Behinderung - disability
I hope this helps a little. make sure you charge the battery fully, Germany to Croatia is a bit of a drive for the lad | 