Your search for "plug cap" revealed the following:
Lambretta Original Style Spark Plug Cap
$7.99Original style spark plug cap for all models. INNOCENTI 15017070
Lambretta Magnetic Oil Drain Plug Casa 8001310
$17.09Oil drain plug with magnet by Casa Lambretta 8001310
Scootopia Lambretta Disc Front Brake i Cap
$12.99Scootopia Lambretta disc front brake i cap for TV SX and DL GP INNOCENTI 19744064
Lambretta Legshield Beading End Cap Set for Series 1 and 2 15050063 15050064
$16.99Lambretta series 1 and 2 top & bottom legshield beading end cap set by Scootopia INNOCENTI 15050063 15050064
Lambretta Choke Mechanism Top Hat Cover 19015023
$15.99Lambretta choke mechanism top hat cover INNOCENTI 19015023 76760832