If it goes back to the 50's, it will be next to impossible to get parts. Some parts may be available in Europe.
I would check to be sure it was as complete as possible, then buy it anyway as the early models are becoming rare.
Any Solex from the 3300 series forward can be repaired with currently available parts. Velocruz.com has most of everything you'll need for the later models.
Don't expect any Solex to be fast. They are about getting there and back in the most economical way. but they are fun to ride. I got 3 of them and a Micron scooter.