My Seagull came with a broken throttle cable: the carburettor end was missing.
So I went to the local motorbikeshop and bought a (moped) throttle cable and a new cable sleeve.
I took my (16 Watts) soldering iron, removed the tiny ring from the original cable and soldered it back onto the new one.
One snip with the wire cutters and the job was nearly done:
I used a locksmith's file to remove the excess solder and that was really it !
(As one can see I had to re-use the original sleeve-ends, since the new ones were a fraction too large to fit both carb and lever)

And guess where I found plenty of NGK A6's, SAE 140 and starterrope-by-the-meter?
... In the local lawn-mower shop !