It seems that the Swedish Vespa importer "Como M & T Bjerke AB" discovered the side cars for Vespa early on. Here are two leaflets or sales brochures from the early fifties.
The "greenish" one above should be from 1951-1952, the Vespa being a "vacanze romane" (Roman Holiday), the nickname came from that movie.
Below is a "faro basso", Vespa 125, also with a Piaggio side car. On the leaflet it says "Vespa mod. 53 med sidvagn och inbyggd hastighetsmätare" in Swedish. Meaning that it is a 1953 Vespa with side car and speedometer", although there is no speedo on the handle bar in the picture.