By coincidence we recently came across the Bromley Bubble Car Company in Great Britain, a company that deals with miniature cars and then with the Isetta in particular! For example, they restore these trolleys and have a large warehouse with new (!) And used parts.
It is also difficult to (re) make parts that are no longer available. A handy address in case you run into problems? Further information: telephone 0044-1795-843.580. It is also located at Newington Enterprise Center, Unit 11a, Wardwell Lane, Newington (near Sittingbourne), Kent.