On the Dutch online Marketplace I spotted someone offering various NOS clutches, including this one.
So I purchased them immediately, thinking my ISO was a 150 tipo F. Although the package says 4 pieces in Italian it only contained only 2. If I see it correctly there are at least 3 required - item 25 in the diagram. In the part nr list there are indicated 2 different nrs, 200074/A Fino al motore N 3300 and 20223 Dal motore N 3301
I knew the first series had a slightly different engine and apparently this is one of those items which is different - despite it's a 150 Tipo F
As for the company Surflex they still exist today: http://www.surflexclutches.com/
And I was able to lookup the clutches for the ISO models. On page 2 you will see the clutches for the ISO scooters:
http://www.surflexclutches.com/Surflexclutches.com/Classic_files/Iso%20%28Veterane%29.pdf
For serie 1 in 1957 they list 48 M 11 and for series 2 (called Diva) from 1958 - 1962 its 48 M 13
And apparently all of this is still available and listed in their pricelist:
I'm not sure regarding the condition of my clutch but this is good news. I will keep this package for nostalgic reasons.