Hi Franco,
I wrote an article in Issue 118 of the Dufour News (available in the archive) regarding replacing the sheaves and the shaft, this may be of help once you have sourced the sheaves. If your genoa blocks are they same design, then they are Lewmar Type 1 but type 2 sheaves still fit.
I bought the sheaves via EBay from Yachtparts based in Plymouth. I suggest you contact Yachtparts and ask if they can still supply them.
I hope this helps.
Jeremy