Welcome to the forum. Where are you located?
Please start by educating yourself on bodges -
Bodgespotting Don't look at shiny advertised scooters without asking yourself (and us) "is it a bodge?". Huge topic in itself.
There are a number of facebook groups for Vespas and classic scooters generally, including a number of buy/sell groups.
Australian Scooterists - classic riders
https://www.facebook.com/groups/171755536248935
Australian Vespa owner- Buy Sell Swap
https://www.facebook.com/groups/3101625213205829 and a few others.
If in Vic Goetz regularly has one for sale
https://gnclassics.com.au/
If in Qld Danny has them regularly for sale
https://www.facebook.com/profile.php?id=100005754046355
If in Sydney Sandy at Scootermeccanica (as mentioned by Steelbytes) has some for sale too.
These are just off the top of my head, all very reputable trustworthy people.
Are you looking for anything in particular?