Bowden cables for the Bella can be obtained from www.moped-garage.net. They carry pre-fabricated cables for the starter, gas-handle, brakes etc.
When I tried to order they did not ship to the UK so I had to use a postbox service to provide an address in Germany. They do ship to countries in Europe their side of the channel. They go for about 8 to 10 EUR each; for the time that saves me making bespoke ones I think that’s a bargain.